I have also heard they are more trouble then they are worth unless you know what to watch out for. The main issues from what I have read about them is that the debris gets trapped and will eventually sufficated the BB if not removed or something along those lines.
after a few months of operation, the gravel begins to pack with so much silt and dirt that circulation stops and the bacteria suffocate. Since the filter still appears to be working, water quality deteriorates, usually unnoticed until it is too late. If the tank is medicated or overfed, an even more rapid die-off of the culture may occur. A speedy water change may avert disaster, but this is the sort of headache and frustration we are trying to spare our customers.
Thats from an online shop, not sure how unbiased it is...
If it were me, I would either get a HOB or a sponge filter. If you were also given an airpump and airline tube - go for a sponge filter. I seldom see them in stores but you can find them on ebay or amazon for pretty cheap. Be sure to also get an attachment that lets you adjust the airflow. I have both sponge and HOB filters myself. I use the sponges in divided tanks as I can hook up multiple filters to each pump. I also have Tetra 10I filters and Aqueon 10 quietflow filters. The only real difference is the sponge filter will not do chemical filtration as it has no carbon.
Supposedly Hydor sponges are the best but I have a Deep Blue sponge and won a lot of 6 small sponges via a seller in Asia for about $10.
There is also this kind of "sponge" filter