On the 3M Paint Defender spray, here are a bunch of reviews which are decidedly mixed:
Lot's of complaints about short longevity and difficulty removing...
SCCA & Midwestern Council W2W, '91 Spec Miata, '07
NASA TTD Champion, Midwest, '99 M3, '09
Midwstrn Council TT Champion, BS, '10 GTI, '10 &'11