Well, it's negligibly slower than the Galaxy S IIIs S4 Snapdragon. The only real downside is the lower resolution display.
This is hands down the best no-contract phone (and deal) out right now, though. Especially when the phone is still going on eBay for around $400.
I would advise against buying phones on eBay.
Much of the time, people get these phones cheap on credit and then resell them "new in box" on eBay. I have heard of a few nightmare stories where the original seller stopped making payments on the phone to the dealer and the service provider voided the ESN, essentially bricking the phone. Even though the phone may be new-in-box, the connectivity of the phone is dependent upon relations between the original buyer and the provider that the phone is linked to, which is something that a buyer on eBay would have little control over.
If you're in the budget for an SII, I would recommend the Galaxy Nexus. All around, I think it's a better phone and you can grab one completely unlocked from the Google Play store for about $350. You'll get an unlocked phone with customer support from google and you won't have to deal with crappy dealer bloatware slowing down your phone.
Phone spec comparison:
Google Play store: