I have one of those so called Hybrid Pools. Mine was built in 1978, I believe. It has the fiberglass walls for 3' all the way around and then concrete for the bottom in the shallow end and walls and bottom of the deep end. I don't have any complaints. I've only lived here for two years but it seems to be fine. I have noticed some hairline cracks in the fiberglass walls in some spots. Not sure if that will be a problem or not. Doesn't seem to be now.