I bought my first one (one of the 1400lph models) about two years ago and have since upgraded to the 2000lph ones on all my other big tanks.
There are one or two points to bear in mind;
They're cheap, so some of the parts (specifically the handles on the media baskets) are quite flimsy, although the newer models are much better, but you just need to be gentle with them.
You
must fit at least the sleeve for the UV, even if you're not going to use it, as they leak if you don't!
The stated flow falls off a lot once you have them filled with media, but that's true of nearly all filters on the market.
I'm very, very happy with mine and would recommend them to anybody.
EDIT: Oh, you're talking about the internal filters
Doh, sorry, never used them; get an external instead! Much more space for media and frees up space inside your tank!