I did some calculations on the package for other workshop, autosaver. Find out I can't really save much and if I encounter any small problem, I got to pay even more if do outside. Just 1 small thing in the 2 year possible to pay more already. If take NPMP, got any problem somewhere with the car (funny noise or whatever) can just complain to TC, most of the time they solve for free. If you do outside, may have to pay to change this change that and there's no guarantee.
Had many bad experiences with external workshop, especially those small shops.