I just bought the Wavemaster XXL. I was reluctant to buy a water/sand based bag but the beams in my house were taking a beating. I first saw the XXL at my kickboxing gym and thought it was great. I now have one in my basement and love it. It's got a huge surface area and the base doesn't get in the way of low kicks. You can find them on eBay for $185.
Carpetlion probably got a defective bag and base. If so, you should contact Century and get a new one or a refund. The two XXL's at my gym have been performing fine for the last 1+ years. I'd imagine a bag at a kickboxing gym is going to get much more wear and tear than one in someone's home. Mine is performing fine at my home.
The base does not preclude me from throwing low kicks or side knees. The only strike I might refrain from throwing is a flying knee for fear of landing on the base.
I'm more interested in experiences with bags like the Fairtex freestanding bag. Anybody have one like this? I want something I can work leg kicks on. The typical water/sand bags don't cut it (too high). The more banana bag like, the better.
I have the wavemaster xxl, it's good for kicks and fist and elbow strikes. Not so much for knees because of the base. I filled mine up a little more than 3 quarters full and it's seems about the perfect amount. I thought it was kinda pricy at $225 and not near as good as a hanging bag imo but if your options are limited it does the job