It doesn't have the best track record to be honest. It's not the sled chassis, the chassis is very successful even in 2011 as it is the IQ chassis. The problem is the engine. The 900 engine was a failure for Polaris, hence the reason it was only available for 05 and 06. Not all of the 900s were bad, but many were. If all the recalls were attended to and the engine of the Fusion you're looking at has had no prior problems, it very well could be fine for you, since any Fusion 900 in 2011 likely has had the recalls fixed to run correctly.
Yes. The 900 engine is the problem, and if you can spring for the 07, its definitely worth it. No major upgrades to the sled over those years, but its a better engine. It's got about 130 HP compared to the 150 from the 900, but that is still strong.