I’d say you’re right if it was the pan or tub surface but if poster is only concerned with the walls then it would probably be great for the 4-5 years he/she expects to be there.

My experience differs. I've done 3 - two over tile and one over a fiberglass insert. The fiberglass one was really great and after 5 years is still going strong. The tile less so but still pretty good. The tech filled some tile cracks and made them virtually disappear. He did a really detailed job on taping, sanding and spraying and the result was excellent. Now a few years later the finish has dulled somewhat but no peeling, cracking, etc. It was only promised to be good for 3 years and it beat that forecast and I can have it re-done one more time. At a cost of about $450/bath (~2017 dollars) it was a whole lot less cash than new tile, even if I did the work myself. So I guess there are other factors at work - maybe the tech's competence of the quality of the substrate or whatever - but my mileage varied from your yours. Cheers!