hi .. i use both retro 100 and 400 in 120 ...
as already mentioned by members :
both the 100 and the 400 seems to be coated on exact same base ... in comparison to apx100 the base is thicker and a bit less clear (just a bit) and reminds a bit the apx400 base (but doesnt seem exact)...
curling of the retro (both 100 and 400): i can see that after just couple of days curling is no problem at all, and a couple of weeks of storage it is quite perfectly streight.
immediately after drying: it depends on drying conditions (water, air, time). basically, it is "normal" and not much different from ilford fp/hp curling, and not as good as say acros or tmy-2 that come very streight rite after drying. still, i dont see it as problem... the apx was curling too, and if i remember properly, even a bit more ...
now about quality ... nothing much to say ... for me - the KING of black and white films ... ya, it is apx100... though apparently not the same base, but the results are as seductive as was apx100... (the same about 400 too).
i dont have a single roll of original apx100 any more, so i cannot make side to side comparison, but no need for it ... developing times are the same basically, and the look is unmistakably - apx100.
rodinal is a natural choice for this film... and so is id-11/d-76 ... try both. rodinal will give bolder look with a little grain (in 120 u will need to go for serious enlargement to see that beautiful grain of this emulsion in rodinal). id-11/d-76 will give a cleaner, smoother and sharper negative.
the differances in developer choice are more dramatic with retro 400 ... id-11/d-76 can push this film to 800 very well if u need the speed or the look of such push (honestly i was not doing it with apx400, but now rediscovered this emulsion and its fantastic push look).
quality of product... no problems basically.
apparently, kodak and fuji films seem to have better product quality and control and so iflord ... i would say - reminds efke (also one of the fines emulsions).