I have fired approx 5000 rounds from each,it makes no difference if I own one or not,compared to the AR15/M4 carbine neither offers any advantage other than compactness.
In fact the FN2000 was rejected for lack of reliability in the Croatian Army trials, and has not been adopted in any great numbers in any military due to reliability issues that may or not have been corrected at this time,the fact is it did not add any advantage to existing systems. The integrated G/L and sighting system has promise though.
The P90 fills a niche that for the most part doesn't require filling the PDW concept is flawed and has not caught on outside of certain Special OPs units where the P90 is used in the traditional SMG role, not so much that of the PDW.
The poor performance of the 5.7mm AP round has been well documented so no need to rehash that. A 5.56mm Carbine will give better performance without having to create a separate logistical chain for a new caliber.
The complicated feed system and magazine design is prone to fail as well, in one afternoon of shooting 3 magazines were rendered useless, not exactly confidence inspiring.
The civilian versions I have limited experience with only about 400 rounds through each, but no significant improvements were noted.
So there you go...Meh.. nothing to write home about and definitely not worth the cash,I'll stick to my AR15 FOW thanks,and leave the FN 2000 and P90 to the video game fanboys.