Unless you are in the habit of shooting gritty bullets through your guns, firelapping results won't resemble your normal barrel wear. It does reconfigure the throat and bore diameter a little.
A truly worn throat has a lot of stress cracks on its surface due to the surface heating faster than the substrate metal. This cracking makes the alligator skin pattern you see on old throats and up the first inch or so of the bore. The cracks define little squares of surface that eventually start to chip off, leaving the throat asymmetrical, and that is what causes accuracy to fall apart.
Firelapping doesn't do any that because it isn't particularly hot (the loads are very light) and its action is symmetrical. It will cause the point at which a bullet touches the throat to move forward. I measured about 0.001" forward throat move using a military throat wear gauge when I firelapped my old DCM Garand. The bore widened about 0.0005" at the breech end, which was good, because that was the amount by which the original bore was constricted at the breech end. It was not enough to bother jacketed bullets much other than to make copper build-up faster, but lead bullets didn't like it at all. The muzzle opened up about 0.0001" in the process. I can't say the gun shot any better than it did originally and without copper build-up. But it did stop the copper building up significantly during a match, which had been causing groups to open up starting at about round 40. So it made the accuracy last a lot longer between cleanings. It also made cleaning dramatically easier. It originally took me about four hours of constant reapplications of Sweets 7.62 (this was the early '90s and before the Bore Tech products I use now came out) to get patches to stop comming out blue. After firelapping I could get a 50-round match cleaned out of the bore and the gun lubed and ready to put away in about fifteen minutes.
Tubb's kits are just a form of firelapping. He likes his abrasive selection better than some commercial kits and he is lapping with jacketed bullets, which tend to straighten the bore some, too, where BHN 12 cast bullet lapping tend to taper the bore wider at the breech and narrower at the muzzle. But I have used both and feel I can get a good job either way with a NECO kit (it can be used with either cast or jacketed bullets).
Tubb also has his TMS kits. These seem to be the finer Final Finish bullets for throat "touch up". He says he can double barrel life by using this approach. I haven't put enough rounds through any barrel I've used his kit with to see if that matches my experience, though I have one getting close.
