Availability probably depends on where you are and hang out. All of the gun shops here in Tulsa have it....none of the Wal Marts. Quality...mine is really accurate and I like that the bullet will not penetrate walls, etc. as readily as other rounds but will still get the job on target. The Secret Service uses the 5.7x28mm round. Originally designed to defeat Soviet body armor at 75 meters in urban situation with the black tip ammo (banned....can only own what was in stock prior to the ban). Also...I recently saw 2,000 rounds at the Wannamacher's Gun Show for $729 cash and carry including tax. Very competitive with 5.56 prices...same bullet diameter.
My wife likes it because of lack of recoil and ability to stay on target. Now...it's readily compared from the pistol to a 22 magnum from a rifle (from the PS-90 it's at the bottom end of 22 hornet) Gun-haters in congress want to ban it...all the more reason to buy one. Also loads up 20 rounds to the mag.
I get it locally at $18.50/box of 50 rounds at OPS. Lot crying went on about price 2-3 years ago that dissuaded some...but at todays prices the 5.7 price stayed flat. Two rounds readily available...40 gr poly-tip VMax and a 28 gr aluminum core hollow point. Some rumors drifting about that the aluminum core penetrates armor at close in range.
Light recoil is a plus as well as the fast burning powder...the thing supresses much better than other handgun's. Cons....one basic model pistol and carbine. The PS-90 has a trigger that terrible. The 5.7 pistol is much better. Also...I like the position of the controls on the 5.7 better than traditional handguns....it has the safety up front where the trigger finger is supposed to be when it's not on the trigger. Danged expensive to buy and only FN has them....