A normal filter provides mechanical, chemical, and biological filtration as well as providing some current. Some powerheads have a sponge to provide some mechanical filtration but are just typically used to provide current.
It depends on how you use the powerhead, you can fill a intake tube up with media utilizing chemical filtration, the sponge on there for mechanical filtration and then the gravel itself for biological.
I use RUGF's and use powerheads alot, just picked up 3 dozen more, some work some dont but for 10 bucks Im not complaining.
What are you thinking or using it on now?
Every tank of mine has a Powerhead in them now and the water has never been cleaner.