Users experience with Sumps on non-drilled tanks?

[johnnytaboo]

So after overcoming my initial trepidation about sumps when I set up my 144 tank, I'm looking to add one to either my 120 or 180 (both tanks have 2 FX5's running on them). Problem is, neither of those tanks are drilled, so I would be using a hang-on overflow. I've read a few negative things about these, so I was wondering what everyones experience here was like? Anything I should watch out for, be aware of, anticipte, ect?

Thanks for any help!
John

EDIT: I've been eyeing the wet/dry filter in the link below for a while. Thoughts?
http://www.ebay.com/itm/AQUARIUM-12...177587238?pt=Fish_Filters&hash=item2586eece26