I have a 1988 560SL that has an Ungo alarm system that does the keyless entry/exit option you speak of. Also, the Ungo system automatically closes the doors when you put the car into reverse and the system has the option to open your garage door, radar sensor to protect the car with the top down and carjacking. I happen to have all these options and have enjoyed them the last couple of years. Hope this helps.
I have the MS5000 model. Nothing in particular that is unique for the installation. I had it installed at my local alarm place. If I had to do it all over again, I just wouldn't install the carjacking feature since from time to time, I would open the car door while the car was running and this action would activate the carjacking feature. Other than that, I have been very happy with the useful features of the Ungo.