Just finished a free 7 day trial and decided to purchase. Very impressed with the speed increase for text and bulletin board type work. Graphics not so great, tend to be blocky at max speed settings, but these can be improved by reducing speed.
I bought it primarily to speed up my connection when travelling with my lap top, as none of the hotels we stay at have high speed internet access.
Works by your request going to their server ,which retrieves it for you, compresses it and sends it to your computer, where the software decompresses it.
If you can get broadband pay the extra, if not a very credible alternative.