My .02
It's an overpriced .22 that looks "cool".
The 5.7X28 is an unproven manstopper. The P90 is a "niche gun" designed for a "niche role". 9mm based subguns like the MP5 are great for CQB but wouldn't penetrate body armor. The 5.7X28 (at short range) will penetrate armor but the terminal performance is severely lacking. The wound channel is far too small (think icepick). Even with the ammunition designed to make it partialy effective it has experienced many problems failing to provide adequate stopping power. Civilians are unable to even get that ammunition. While the BG may eventually bleed out, I'd go for something more proven to do "more with less".
BUT
Not meaning to rain on your fun with a cool new gun....If you can afford it and you enjoy shooting it there is absolutely nothing wrong with THAT and in a pinch, well, I wouldn't volunteer to get shot with one. I would prefer an M4 myself.