I had a one piece acrylic aquaglass tub installed in my home approx, 18 years ago. Aside from a small crack on the edge of the ceiling of the tub that happened when the tub was lowered into my basement before the house was put on top, I have had nothing but good luck with my tub.
May be the difference between gelcoat and acrylic, and the crack was up so high that I didn't even have it repaired, or it may be that the older units were built much better, but I haven't had any problems. Also, I work for a plumbing contractor and we almost always put a small amount of quick crete (concrete) under the base of the tub or shower, and that alleviates the problem of the flexing in the bottom of your tub / shower. It may also be that the contractors seem to get better quality than the big box stores.
Sorry so many of you have had problems, but they used to make a quality product. We put many of those units in and I don't remember more than a small handful of problems with any of the aquaglass units.
Product or Service Mentioned: Aqua Glass Bathtub.
Reason of review: Good quality.