The two-way remote can be installed in 2008 Malibu's depending on which model you have. I have to AP3 one, and I got it installed by my dealer in July. It cost me $227.00 at the Friedley, MN Chevy dealer. Took only about an hour.
The range improvement is not too impressive. I would say that it is only slightly improved. If I were to estimate the range, I would say about 150 feet at most (clear line of sight). There is an antenna that the dealer installed in the rear windshield right beside the c-pillar, and if you're trying to start the vehicle with the rear facing you, the range is improved. I am however quite dissappointed with the GM version as my Viper remote starter on my Mazda3, starts my car well over 700 feet away.
What I do like however, is that the screen displays whether or not the car is locked. Sometimes, I find myself wondering if I locked my door, and with the display (as with every other two way remote), it tells you the status of your car. As for the panic button, if you press both side buttons at the same time for 1-sec, the panic alarm is activated. It's actually easier to initate the panic alarm with the extended remote, as it works further away, and is quicker to respond.