Those RPM are very rough kits, but buildable. Many of them are mix and match, by that I mean they add bits & pieces from various kits to similar hulls. You'll get several different colors of sprues molded in different grays, white, off-white, tan and some sprues are marbled (where they mixed colors).
The parts are thick, about the scale thickness of a man's fist. Construction is mainly flat pieces that have to be aligned to form the lower hull. Same deal with the upper hull superstructures. The super set I have includes assembly instructions for just about every version of tankette based on this hull that they made a kit of. The paint and markings for the kits are limited to a small view of the left side of each vehicle.
Aber makes a couple of PE sets, 35016 & 35017, for the TKS and TK-3 respectively. They are expensive and hard to find, but add greatly to the kits.
There has been a lot of mold swapping in Eastern Europe and each kit has appeared in various companies' boxes, so if you do see similar kits but from different manufacturers, most likely it is the same plastic inside. Just go for whichever is cheaper.
Some of the kits come with rudimentary interior sprues. Basically just big white boxes, seat and a steering yoke. Again, the part thicness will jump out if hatches and doors are posed in the open position; instead of inch thick armor, you'll see 6 inch thick armor.
The kits I have on hand are the RPM TKS and TKS with interior, and the RPM T-26T artillery tractor based off the British Vickers light tank (7TP/T-26). I also have the Aero Plast Tankieta Super Set (best value if you can find it) that gives you the option of building the TKS, TKS w/20mm, TK-3, TKW, TK-SD. It's the RPM complete set of mix and match parts all stuffed into one box. Best part was that I got it from Great Models a while back (2003) for $7.40. It didn't have the interior sprues though. The Aber set for it I ordered at the same time was $11.10.
Feel free to shoot me an email if you want a scan of the instruction sheet.