Havent had one installed personally, tho a couple things a buddy told me to consider (he worked for a fairly large electronics company here in cowtown)...
1) There is alot of cutting and splicing into the harness to get them to work.
2) Their reliability may not be the best, because of that splicing and cutting.
3) Do you really want some minimum wage monkey screwing with a fairly important part of your car...
Personally, Id much rather a factory remote start (no matter how annoying) and keep my warranty, than go with something that functions right but very possibly could TKO my warranty.
Oh, and im actually looking at a Python 872LE for the mustang, and
was my reaction to how much there is to connect to get it functioning...
2012 Tuxedo Black Ford Focus SE
1984 Copper Metallic Ford Mustang LX
Gone but not Forgotten:
1992 Beige Dodge Spirit SE