As far as the Kel-tec Sub 2000 goes:
1. sights are in the way of optics, and you have to cut them off to remove, they are molded in. Which is the same gripe I have about the Berettas.
2. Action can fire when unlatched.
3. Poor accuracy. No better than a pistol at 100 yards.
4. Lousy ergos
5. poor trigger
The idea of a carbine that can take popular pistol mags is worthwhile, but it's just not that usable, IMO. There are better options.
A carbine would be a 100 yard tops gun anyway, thats irons for me. Interesting on the firing part, I'd not be wanting to have it loaded while its folded up though? DUnno, have to look into that.
My pistols are pretty accurate at 100 yards generally speaking so its going to be the same then. Plenty good enough to smack a deer if you can hold them well enough.
Ergos, never really mattered to me, we started in service rifle, and as such had to learn to adapt to a fixed gun, and so we can manage ergos.
triggers, that would be an issue for me. Hate bad triggers.
But a fun thing to play with though just to see how bad or good they really are.
But alas to much other to spend money on right now... still want a colt sauer rifle once in my life. Need something big for the big AK bears when we move up...458ish need a backup glock 20 SF so we have one there and one here in the winter... love how the 10mm smacks deer. Still working on finishing the sheep rifle... and so on... and short on cast bullets for pistols and need another 100 pounds or so of powder to stock up on... LOL