From that I have read/seen the 501 is very similar to the tom aquatics mini filter. I have a tom filter and after a couple of months I wouldn't have trusted it to filter a 32oz cup of water effectively.
According to the manufacturers spec sheet, yes a 2211 would be too much for your tank but in the real world, no it isn't. It would be perfect. I am using a 2213 (I think eheim says its good up to 59g) on an ADA mini-m (5.5g) and it works perfectly. I also run a 2217 (eheim says its good up to 159g I think) on my ADA 60-p (17g) and again it works perfectly.
My filters do have the eheim quick disconnects which have flow control knobs on it so even if the filter would have been a bit too much I could have turned it down a bit till debris and mulm from the tank got in it and flow was decreased a bit. I don't know if the 2211 has those but im sure you could get some. They are a must if you want to clean the filter easily.
Also another wonderful benefit to using a larger filter on your tank is that the need to break down and completely clean the filter for maintenance is delayed by quite some time. This all depends on how you stock your tank, plant density, what media you use (if you can get one pre loaded with Eheim media go that route, its good stuff), and other factors but on my 60-p I hadn't cleaned the filter for 6 months (because I experienced no flow loss) so I decided to break it open and check it out. The filter hardly had any detritus in it and now I am completely confident that I can go at least a year between filter cleanings.
