I fly two light aeroplanes regularly, one with Rosetta one with Classic.
It's an excellent system, significantly aiding situational awareness, so long as it's well integrated into your scan, and not treated as the only means of traffic awareness and avoidance.
It DOES NOT see everything - offhand it sees about 3 times as many aeroplanes as my Mk.1 eyeball system does, but about every fifth aeroplane I see out of the window, PAW does not.
The Rosetta does seem to see less traffic than the classic, but the installations in the two aeroplanes are somewhat different, and odds are that's the reason, not the units themselves.
G