I put bathfitters in over 12 years ago, but only the walls.
At the time, they were the only game in town, but times have changed.
Bathfitters would no longer be my first choice, check out a company called Re-Bath. Similar concept, but enough differences that it is, IMHO, a superior product.
The problem with repainting a bathtub is that the enamel is not baked on. A good paint job will last 6 or 7 years, and often bubbles. A bath tub insert, if measured and installed properly should not move around.
While new tubs are certainly not terribly expensive, I can tell you from personal experience that to get a tub out is a pain in the ass that means breaking tiles, putting the new tub in and preying that the damn plumbing lines up (which mine did not). I finally had to call in a plumber which was frigging expensive as it was a 2 day job to simply change the plumbing and install the tub that I had purchased. I was still left with walls that had to be repaired.
I would still have the bathfitters, except the damn thing no longer fits because of the new tub. I had no issues with bathfitter, but if I was to do the acrylic, I would use Re-Bath now.