I feel that the whole point of the P90 is the small form factor and the full auto combined with a small fast projectile that is unlikely to over penetrate. Given the longer barrel and lack of full auto of the PS90 you might as well get a five seven for home defense if you want that Gucci factor.
I'm not any kinda fun person. But I did once get a chance to use an FN FiveSeven at a range once and it was fun. I was shocked at how much more I liked it over the 9mm's.
Really unlikely. The whole point behind the P90 was as an alternative to 9mm and FN decided on 5.7x28mm. I've heard of (9mm) M11s being modified to look like P90s...maybe that's what you saw?