I've spoke to a few tuners who have said they wouldn't remap a car that had a Littco turbo. The main reason seems to be that something like a map from REVO has had hours and hours of testing done on the stock IS38 turbo. The Littco L380X is slightly different and introduces a tiny amount of lag (not noticeable) but gives you more boost/flow at the top end. I think tuners are concerned that their maps won't be as effective on something untested. I had one turner tell me they would tune it, but couldn't guarantee the results.
Like you, Ive had a tuner try to steer me towards a Turbo Technics turbo, but I think that's only because that's what they work with and know. My tuner, and another that's fairly local both work with Littco, so if you go to them that's what they suggest. It all depends on the tuner. I don't think these tuners think there's anything wrong with Littco turbos, it's just that they are not familiar with them. The tuner I used know the guy from Littco and has helped out and done testing for them, so it seems obvious he'd stick with them.
As mentioned, I've had a nightmare with my car. But after a lot of research to speaking to a load of tuners, I'm confident that the map itself wasn't the cause of my turbo failure. It's more likely that my stock IS38 was balanced within manufacturer tolerances, but possible just. Once the turbo has been asked to produce more boost, it's just given up. My problems would have ended there if the recovery guy hadn't have tried over and over again to start the car to get it onto his truck, as we believe this is where the damage to the crank bearings has come from. When he was turning it over, we heard a metal grinding noise (probably a spun bearing).
Cost wise, I think I'm up to around £3k to get the car back on the road. That included replacement turbo, and new crankshaft bearings and seals. If I had only needed a new turbo, then £1200.
I keep seeing posts online saying get a REVO map, don't go independent. But if you do your research, you'll see that turbo failures occur on REVO maps as well, although I think any turbo failure is less likely these days compared to when the Golf R etc first came out as VW have made various changes to the IS38 over the year in an attempt to reduce the number of failures, but I think still the underlying issue is there, just nowhere near as apparent.
The only advice I can give to anyone remapping the IS38 turbo is, don't floor it until the engine oil is up to speed. There are those that believe that these turbos fail because of a lack of oil supply to the bearings. If you're flooring it when the oil isn't warmed up it won't be flowing as well through the turbo and won't provide the required lubrication. The second bit of advice is, listen out for any sort of whine coming from your turbo as low revs, as this is a clear sign that the bearings are warn. I had this noise, but I just assumed it was something to do with the remap. I could kick myself that I didn't do anything about it and get it looked at sooner.