it's just a normal disclaimer that any aftermarket shop will put up to reduce their liability. think of it this way: they are just providing the service to install parts/perform labor. anything that happens to your car as a result of these aftermarket parts is entirely on your head because you chose to have it installed.
i had my mk6 flashed by NGP, no worries. great bunch of folks over there who are honest and do it right the first time. countless others here and beyond can attest to that as well