Quotes found here and there are fine. Real world experience is quite different.
Full length dies are just that. They size the whole case. They can be adjusted to increase case life by not pushing the shoulder any further than needed in your gun.
Neck sizing dies are just that. They size the neck only. The bushing type neck dies are obviously more versatile.
Body dies are made to size the body of the case without sizing the neck. They expect you to do that in a separate step. They are made for the folks who are not bumping the shoulder back and are neck sizing only. Those cases will eventually get hard to chamber and the shoulder must be bumped back. (This is not the better way to do it in my opinion. Bumping the shoulder back a thou or so every time as you size the neck while supporting the body is the way to go as far as pure accuracy goes.)
If the Forster die will bump the shoulder properly while sizing the neck it is machined to lightly contact the case sides or it won't work. Since they make them for everyday rifles the tolerances in stock rifle chambers would be to great for it to be the best way to go.
My "bump die" (that accepts carbide neck bushings) was cut with the finishing reamer that cut one of my old Bench gun barrels chamber. They are all so close it still works for the two barrels I have now. It contacts the case body but will not size it enough to measure. It has to be constantly adjusted to match the "springyness" of the brass as the brass ages. When you are trying to bump .001 every time it is critical to check it every time and adjust as needed. This is a pain, but necessary, or you will end up with brass that is hard to chamber and then hard to get out. You don't have time in a match for that, period. (7 minutes to shoot 5 on the record and only 15 to 20 loaded rounds - They must work.)
Maybe the Highpower guys who bring lots of loaded ammo can afford a couple they have to put aside. The bump them back when only when they get tough may work for them. I don't know though. I would have to ask USSR or Slamfire, someone who shoots that game. It is different than Benchrest. We are after extreme accuracy at 100 & 200 yards, and that's it.
Those that want to load match ammo need to go to a rifle competition and see what "Match accuracy" really is. Those guys will help you obtain it, but be ready to get your feelings hurt about your rifle/ammo/etc. I thought I had a couple of accurate rifles (and they were) until I went to a Benchrest demonstration near me in Greenville Al.
Wow
I had to have one of those rifles. I was hooked big time.