As far as emulation, PSP emulation is pretty spot on, but so is the DStwo. The one category where I'd seen the PSP fall flat though is for the TG-16/PC Engine emulation. The best recommended TG-16 emualtor for the PSP was clunky and ran poorly, while nitrografx ran through a DS flashcart (didn't need any DStwo-specific features) was nearly perfect for me, including being able to run Rondo of Blood and TG16 Ninja gaiden, which wouldn't run at all for whatever reason on the PSP PCE emulator.