Extremely impressive collection, OP!
I only have 2 bullpups...
The KSG was in the same "gunshop availability" situation just a few years ago. Everything from Kel-Tec goes through the trickle-down effect. Unfortunately I haven't fired a Kel-tec bullpup rifle.
I have played with, fired, and worked on the Tavor and I don't really like it that much. I thought I wanted one for years (I guess since Resident Evil: Apocalypse and Rainbow Six 3), but when I actually got one in-hand it was like, meh. Just not worth the $ IMO.
I also got to repair and play with a Mossberg bullpup, and it was cool, but heavy and impractical. I had to blast with it for a few minutes though, while pretending to be like that one black guy in the original Stargate movie.
lol
And the P90/PS90, while fun, I've just never been sold on it. I'm kinda kicking myslelf for not picking one up when they were $800, but then I look at ammo prices for 5.7 and stop regretting that immediately. Plus I am a big guy, so there's really not much difference in burden of carrying a P90 vs a F2000 or AUG, which fire better and less expensive bullets. If I am to get a PDW with special ammo, it shall be the HK MP7.
I've been eyeballing the B&T MP9/TP9, but everyone tells me the trigger sucks (and my memory of dry-firing one confirms this). I haven't heard of anyone making it better. Perhaps it's possible?