Range extenders do tend to blow unless you're using it as a bridge (line a cisco aeronet bridge) only. Best bet is to use a product (like you bought) with great reviews and decent range built in that does at least N (or AC). Do the comcast modems use only G or did they allow N? When I worked on them they used G and would allow free access so we had to turn them off (omfg so annoying, people in nursing homes were using our access points and when we shut it off, the home complained - whole story). Always turn off the built in wifi and use something better, unless you're really looking to save a few $$$. Oh, and since Comcast started pushing docsis 3 out to their modems, they did get a bit better overall. Just the view they have into the suckers is incredible. LOOOOOOOOOOVE comcast business class, beats the rest hands down for service. For home, product is good, service stinks last time I called, well, when I had internet.