Stereo & Electronics - remote start add-on to factory remote

http://www.directed.com/security/valet/val_rs.asp#561T

valet 561T

has anyone had experience wiht a system like this that adds on to your factory remote? just wondering how well it works so i can decide whether i should get one or not

i have been told by car shops that this only adds on to aftermarket keyless entry and not to factory systems. is this true?

if that is true, then will this one work?
https://www.designtech-intl.com/merchant.ihtml?pid=1&lastcatid=18&step=4

and for the gm bypass thing does it matter what brand you get?

you can get a radioshack brand bypass. 5 cent resistor with the same ohms as the key pellet.

i have been told by car shops that this only adds on to aftermarket keyless entry and not to factory systems. is this true?

if that is true, then will this one work?
https://www.designtech-intl.com/merchant.ihtml?pid=1&lastcatid=18&step=4

and for the gm bypass thing does it matter what brand you get?
I looked through the installation manual and it looks like that unit will work fine in F-bodies as long as you add the VATS bypass, add a relay to convert the positive door lock pulse to negative, and program the module to operate on a double pulse rather than the default single pulse. That way you would press the lock button once to just lock the doors or twice within three seconds to both lock the doors and activate the remote start.