I think you should ask people who OWN the 5.7 if its worth it. Ask if they sold it, or still have it? Ask how the recoil, accuracy, sights, and overall quality is. I think you will get less vague answers. Theres too many members here who are simply too cheap, never fired one, or too closed minded to give a respectable answer worth weighing a decision with.
Usually youll also get many nay-sayers saying the 5.7 is like a 22 magnum which simply isnt true. I have seen deer dropped with one shot from a 10" SBR PS90. I dont think the pistol version looses so much punch to render this round innefective from a pistol platform. People tend to shun innovation, such as Glocks when first introduced.
I sell them and personally own one. I will never sell mine. They are very accurate, great sights, mild-low recoil, and for a gun thats has alot of plastic it is very robust. I have fired about 300 rounds through mine with no malfunctions.
Ammo isnt very expensive for the quality you get. Its cheaper than premium defensive pistol ammo, to be fair there isnt cheap plinking ammo, but you can reload or wait for wolf to start amking some hopefully.