Python Remote start and the 455T module

I have a 98 JGC Limited and am having a Python 1400XP remote start installed by Circuit C_ty.

Am I correct in understanding that the DEI 455T module will allow the Python 1400XP remote to basically function as the factory key fob?

I guess what I am asking is will I still have my factory alarm system, door locks, and dome light feature with these two items?

I was told that if I didn't add the 455T, that I would lose the factory security.

I am having it installed on 12/5 as I was too chicken to attempt it myself. Also, I think it has to be factory certified installed to meet warranty requirements. If I understand it correctly, the 455T saves about 2 hours install time. (Then why am I being charged $35 more to have it installed?????????)

Anyway, any help would be most appreciated!!!

Thanks!

Ron