Ultra Poly One Coat is a reasonably sophisticated epoxy-like pool paint. At the outset let me say I have NO experience with it. I do have experience with other epoxy pool paints. Whenever a gunite pool needs redoing, the choices are clear: paint or plaster. Painting a pool requires some care...you have to insure that the surface is "bondable", so it might requrie the acid wash/TSP routine, or even sandblasting, too. The key is to have a surface that will bond with the coating. You also have issues associated with how wet or dry the surface is prior to painting, and then there's drying time, proper application of the paint (thickness, number of coats),and avoiding rain, and waiting to fill the pool until the manufacturer's specs tell you to. The normal life of a good epoxy job is 5-7 years. I DO NOT know what useful life Ultra Poly states.
Now, the replastering takes some similar care, too, but I think the process is easier. I'll get back to you on costs.