I use these training 'hawks (among others) and am happy with them and happily recommend them. Their shortcomings are few and minimal.
First, they are simply too hard and unforgiving to use for full-speed sparring, even well protected. I suspect that we'd have to use SCA spec armour to make it more or less safe-ish. These training 'hawks are hard and durable and LAST well but, make no mistake, they can hit hard enough to bust bones.
Second, the handle is a bit squarish. Personally, I don't really mind. I tend to not notice that when handling these sort of things, but it's not rounded nor as "meaty" as most tomahawk shafts.
Third, the handle material is the same, nearly indestructible, resin as the rest of the (single piece) 'hawk. This is good for durability but can make for a slightly slick surface. To be 100% fair, the same problem happens with smooth wood so it's not like there's an inherent design flaw or anything. Historically, if this was an issue for the user (sometimes it wasn't) you could carve a "swell" into the handle, abrade or cut grip patterns into the wood, or nail stud the handle. I suppose you could do all of that with these training 'hawks as well, but I chose to wrap the handles with ye olde Friction Tape.
Fourth, it's not quite as "tip heavy" as a true 'hawk. It doesn't have a steel/iron tomahawk head on it so it will be a bit lighter than most. That ain't a bad thing but it does mean that the balance isn't exact. Again, to be fair, tomahawks aren't exactly known for their pleasing balance. It's a tool, not a small-sword made by a Master Craftsman and expertly balanced.
I've made some training 'hawks from oak and have many of the same issues with them and, further, I feel that the oak won't last as long as these.
The Scalping Knife looks like a great addition to your lineup.
Has anyone harassed you about doing Bowies yet?
Peace favor your sword,
Kirk