Ok, I have my serious doubts about that "other tuner" based on all of what they've told you...
a) I'm not being personally affiliated to Littco in any way, but since I trust owner's feedback above any tuner's own claims, the experiences from Littco owners in forums don't echo at all the claims about cheap chinese items or worse, a bad performance/reliability.
b) Every log of stage 1 on the gen3 I've seen is hitting peak boost at around 1.6bar (1.55-1.65), that includes the big, proven tuners like REVO, Unitronic, APR among others, 1.4bar is simply a joke. I'm sorry but on that claim alone I would say forget about them and find someone who really knows this platform.
c) There is ABSOLUTELY no reason to be drawn to a stage 3 setup and a cost 3-4K for a blown turbo if YOU don't want that power. Plenty of turbo rebuilders available to provide you with an upgraded IS38 making similar power to the OEM unit (or a bit more) but a much greater reliability.
To me, apart from their unsubstantiated claims about other turbos and remaps, these guys seem like they're trying to up-sell you to a solution you were not interested in the first place just because it will mean more revenue for them, I would honestly look elsewhere.