Biggest trouble with VNT turbo,s is heat , load sof cars use them but they run on that horrible stuff called Diesel ( well not always horrible just ask Audi) Porsche seem to have sorted it but like must things you pay for the knowledge ( Coming from Motorsport which invoved Porsche a few years ago) I saw on a dyno a Flat 6 giving way over 800bhp but giving boost from 1500rpm but teven then they said the turbo,s will only lasy approx 6000km due to the heat in the exhaust housings Diesels engines dont run excessive temps in exhaust housing.
The Porsche turbo is not available yet as a new part yet , but I have a customer that has a 33 GTR that is a engine designer at BMW thats has seen some drawings of some turbo,s with high spec exhaust housings incl VNT workings.
Yes everyone is trying them should be good once the manufactuers sort of the temp problems.