I used the Toms mini on a 5.5 for a long time. It was perfect. It wouldn't have been enough flow for any bigger of a tank. The way they arrange the media kind of blows, so I changed it around a bit. Also, people complain about the tubing, but I never had an issue.no experience with these, but here's a $25 mini-canister filter:
https://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3579+3580+16742&pcatid=16742&r=487
supposed to be for nano tanks, but it's 80gph, so if that's too fast, you may want to impede it by putting a pre-filter sponge on the intake.