Of course the quality of work
Of course the quality of work could vary between dealers. I can say, based on my experience, the frame replacement is capable of providing a result that performs on par with a truck right off the assembly line.
Unless the cab and bed are completely removed from the frame, there is no way to get touch-up paint on every place where rust might be hiding. Something else to consider is that the work includes new bake lines and new leaf spring packs for both sides. The factory leaf springs on my truck broke on both sides even though my truck had never been subjected to extreme off road use or excessive payloads. The new springs at least look more substantial than the original springs - and the new springs don't squeak.
If the dealer does the work properly, it is almost like getting a brand new truck that might last another 10 years. The body, interior and engine on my truck are like new after 11 years and 115,000 miles. Now the frame is theoretically on par with the good condition of the rest of the truck.