The flow rate is ample for a 55g.
You may try googling it and reading. I researched filters before buying my Rena Filstar XP3. Based on what I read is why I bought the Rena. Second on that list would be Eheim. Those are the only two that I would buy. But that's me and after reading quite a bit. Eheim 2213 is good on a 55g as well.

 

I will second Eric, Eheim and Rena are considered better value than Fluval from the information I have come across. Eheim have proven track records; many believe they are the best made filters. Rena have not been around as long so it is still uncertain how they will stand up by comparison, so they may be equally good, no one knows. Their performance is certainly good. I bought a Rena XP3 last summer, and I have Eheims on my other two tanks which have been running for more than 12 years without a hitch.

Byron.

 

I have a Fluval 204 that I really like. I would buy another Fluval.