I personally have met/trained with SKIF black belts here in the USA, The Kanazawa's SKIF Shotokan is a good solid Shotokan organization, but he added several kata to the Shotokan curriculum after leaving the JKA many years ago, starting his own federation, before that he was one of the top Shotokan instructors in the JKA.
The other (Traditional Shotokan karate Union) I know nothing about, perhaps their curriculum is more in line with the JKA kata curriculum and teaching method. I would think that if that is the case they would be affiliated with the KUGB and the JKA. If not perhaps they decided to branch off and add other elements to their Shotokan karate do like Kanazawa did. I will ask my friends there in the UK about that organization. I know members of the Seishinkai Shotokan karate do Union that is based there in the UK. I will pass on any information that I find. Meanwhile you should go and check out both schools classes. Get a feel for it. You will be at an advantage in kumite reguardless of which school you choose, because of your Judo training and knowledge of unbalancing waza.