I do a lot of HOB with sponges over the intake. They're great for keeping the water clean, but, the trouble is, they always seem to get gunked up and stop working at the worst possible time for me to clean them. Except for a big tank/show tank or two, I'm planning to switch all my tanks to box filters and filter fluff. Even if they do get really gunked up, you can leave them til Saturday morning, which is better than having to deal with a clogged sponge over an intake at 9 pm after just getting home from work.
Beyond that, rinsing out a sponge can take a few minutes. Those can add up if you've got fifteen or more to rinse out.
And at the risk of repeating myself, emergent plants like pothos are great for taking ammonia out of the water. The combination of the two should make up for the HOB/sponge combination. (And in the case of multiple tanks, it should save electricity, too.)
I think you could use a powerhead...although probably not with fry (a little too efficient)...
I don't like to use sponges (with lots of air or a powerhead) for mechanical because they're hard to clean without returning the gunk back to the tank.
Boxes work great to capture gunk in the water...in their filter fluff, which is really quick and easy to change (for me at least). I use gravel in them to weigh them down...which also adds a little bio capacity.
I use a similar combo of canisters (with a block of foam over the intake to keep gunk out) as bio filters and HOB (frequently cleaned) as mechanical filters. Of course both do both but keeping solid waste out of sponges / canisters means that they don't need to be cleaned as often.
