Those are two very different designs. The FN P90 was designed to be ambidextrous and comfortable to use but I don't think they put as much effort into the design of that rifle. I have to agree though, that part of the model looks really impractical.
I also always thought those kind of designs look impractical but apparently it really is not. Above are two real life examples with the same kind of design.
I have to agree with the others. It just looks uncomfortable to hold. The grip could be more rounded, and not so boxy to conform more to the hand. The hole behind the grip is for the thumb to wrap around the handle (which I'm sure you are aware). I would make the hole larger and (again) more rounded. Like in the last two…
I don't really see where you changed the design apart from moving some bolts and panels. Also your weapon looks more uncomfortable to hold than the concept - you need to model a grip that will actually conform to a human hand. Those vertical strips near the front of the gun are tactical rails that can accommodate…