Yup, very popular over here. Its the no.1 method LFS uses to filter tanks.
Depending on stock they are great, the only downsides are your losing tank space and maintenance can be fussy if the tanks right up against a wall, you are also limited in terms of media space but for smaller setups they are prefect.
I have even seen these run off air which is a bit more complicated but you can get decent flow for very little wattage. hence why I think LFS uses these, better then a sponge filter but using the same draw.