I have one, but its not a MUST have.
My best friend bought it for me for my birthday
1.Its nice though in the AZ heat, dont have to sit in my car while it cools.
2.The Apexi one I got has a digital a/f readout. It works the same as the autometer ones, but shows a theo. avg in a real number. Better than blinking lights at cruise.
3.It tripps people out when I walk in a store and leave my car running.
On a side note, I had to cut the "run" wire going to the PATS in order to let the remote lock the doors while it was running.
L8r
BJ