This thread is broken off from the discussion on Cold Steel katana-like swords, so as not to derail the original thread. The original thread (and post) may be found here.
Wow!! Where to begin?!?!?
The use of Japanese vs. Korean vs. Chinese swords for the practice of haedong gumdo depends on who you ask and what school/lineage/Federation is under discussion. The largest of the world governing bodies for haedong kumdo (The World Haidong Gumdo Federation, also known as the Daehan Haidong Gumdo Federation) requires the use of Federation swords at all Federation-sponsored events. These Federation swords are made in Korea, are very expensive, and look almost identical to the swords from Martial Art Swords. So, in order to participate in a cutting competition, or to test for any belt requiring bamboo cutting (2nd dan and beyond), you must use a Federation Korean jingum. Technically, you could borrow an approved sword for test or competition day, but of course, this puts all those who do not pony up to buy an approved jingum at a distinct disadvantage.
Other Federations and individual schools are not as strict. I personally use a Cheness katana (made in China) and at least two of my students use Martial Art Sword jingum (made in Korea). It is the weight, balance, style (of blade and handle), and safety that are most important. Any sword brought in to class must be inspected for safety (cracks in the mekugi or handle, wear or chips in the blade, looseness of the fittings, etc.). I also prefer a sword closer to the Korean style, as it fits in with the techniques and tactics of our art better (this will open another whole can of worms, because there really isn't any one 'standard' for shinken or for jingum, but on average, the jingum tended to be wider out towards the tip and have less curvature).
About how non-Korean products are viewed: I admit that there are those 'old school' in Korean styles who would rather buy anything Korean than anything from anywhere else. Some instructors buy all (or at least as much as possible) of their uniforms, belts, targets, and even wooden and bamboo swords from Korean sources. (Personally, I fail to see how a stick made in China would be significantly different from a stick made in Japan or Korea, but that is just my opinion ). Some of this is ethnic pride; some of it is based on the fact that many Korean martial arts instructors are also family-oriented business owners, who know many of these suppliers personally and prefer to keep the business "all in the family".
As far as your question regarding the teaching of Korean arts 'pre-JSA', this is another whole can of worms. Remember that the two cultures grew up side-by-side, with constant interaction through trade and warfare. Their developments in weaponry and tactics often mirrored each other and adapted to each other. So, just as you might be interested in one-handed Korean sabers, you might also look for one-handed Japanese sabers. At one time or another, both cultures used straight, curved, one-handed, and two-handed swords, and swords with one or two edges. Trying to pull a 'purely Korean' art out of the mix (if by that you mean one with no Japanese influence at all) would require going back to 400 AD or so, before there was a Yamato culture. However, there would be no 'purely Japanese' sword arts either, if by that you meant something completely devoid of any Korean or Chinese influence.
As far as the swords that Bruce Sims (God bless him) talked about, I have two thoughts. First, I think the largest number of surviving Korean swords that predate the Japanese occupation were non-functional. These shorter, one-handed sabers that showed up in photos from the 1800's, as far as I can tell were largely status symbols worn by Yangbang officials. They were too short to be of practical combat value and worn too high up under the arm for easy access or quick draws. Those who wore them were not soldiers or martial artists, as such people where greatly disparaged in Confucian culture.
Secondly, I think a large number of Korean swords from this time period were worn hanging from a harness (not from the belt) with the blade down. Over half the swords pictured in the Macau museum display on east Asian swords have rings on the scabbard indicating they were worn this way. This was standard for mounted warriors, and shows a stream in Korean swordsmanship that predates interaction with Japan and draws (no pun intended) largely from Mongol influence. There is a modern school of Korean swordsmanship called Choseon Sebup that uses swords hung in this manner, but the drawing and sheathing motions almost all entail rotating the sword and scabbard into the blade-up position, so the drawing and sheathing motions all look identical to JSA iaido forms.
As far as Korean schools that practice drawing and sheathing as an art, there are only two streams of which I am aware. One is Choson Sebup (mentioned above), but it looks just like iaido to me. The other is Guhapdo, but 'guhapdo' is the Korean word for 'iaido'. The difference is that Choson Sepub claims to be a native Korean art, and Guhapdo acknowledges that it is a Japanese art.
Is a kagum the same as a iaito? Yes and no. They are the same in purpose. A kagum is a metal sword without a live blade, used for practice and training (just like an iaito). However, the official WDHDGD Federation kagum used to be made of rolled steel, so it was hollow, and heavier than a wooden sword but lighter than a jingum. This made it a good practical transition tool to get used to a heavier weapon while learning the mechanics of sheathing/drawing. The current approved Federation kagum is aluminum, so it is much lighter. It gives audible feedback when a cut is properly alligned, but it is lighter even than some wooden swords (I don't like it at all). For the purist (Sukerkin, please correct me if I am wrong) a real iaito is made of aluminum. I think this has to do with the fact that export of swords from Japan is strictly controlled and limited, so if real steel were used in an iaito, it would take up one of the spots that could have been used to export a real sword. Personally, I use an older Federation (steel) kagum (because it was a gift) and a Cheness iaito (because its weight and balance matches my cutting sword) in practice.
As far as how Hanwei, Last Legend, and other Chinese knock-offs compare to the MAS swords, the only thing I would suggest is to find someone who owns one, borrow it, and use it a few times. There is a definite, noticeable difference in quality. The difference is worth the investment, but only if you plan on doing cutting on a regular basis as part of your art/training. I plan on saving up and eventually getting one.
On a final note, I recommend using care with the drawings in the Muye Dobo Tongji. There is no indication that the wood block carvings were done by a martial artist or anyone with knowledge of the swords and techniques used. In several places, the exact descriptions/sizes of the weapons are given by reading the MYDTJ, but the wood-block pictures all use the same identical-looking sword. This has been a source of great frustration to me, also, because it means I can't rely on the drawings for insight into the stances and motions used in historical Korean sword arts.
Well, that was a lot of typing practice, if nothing else. All of this is only the "Sword World According to Ninjamom", so your mileage may vary. I hope it helps, or at least, it shoud get the conversation going so others more knowledgeable may add.