I also want a TAR-21. I don't like the way the FS2000 handles personally. I recently bought a MSAR Stg-556.
I've posted under the Auto/Semi-Auto section of Long Guns here. I also posted under the Optics section of Gear and Accessories concerning the Trijicon TA33G-H, which is what I want to run on mine. I have a review under Technical Articles/Write Ups section as well.
I really like how the Stg-556 handles, although I might be a little biased bc I fell in love with a real F/A AUG as a young man.
I've heard the early generations of the MSAR had lots of probs, but they were corrected in later gens. Mine is a gen 4. The later gens will also accept AUG mags as well as the MSAR mags.
I've yet to shoot mine bc of ammo shortages and I currently have no sights or optic to aim the thing. I have a flat top and the rail was too high. I replaced it and all is good, just no optic or BUIS yet.
Be warned, there isn't a lot of info floating around about bull pups and parts are hard to find. As I build my new rifle I plan on making a point of writing as many articles and info about it as I can.
Some places to start: Ratworx USA and Promoted Pawn. Good luck, and please keep us up to date about your purchase and findings.