There are alot of alarms that would happily support a turbo timer, if you already have an alarm then you should ask the installer for some advise.
I have been told that the most pain in the backside to be compatible with car alarms are the blitz turbo timer.. I have used a apexi TT (Turbo Timer) pen style type with a mongoose alarm (?) before and its dodgy ass... it needed a relay so that it can lock up the doors while the turbo timer happily hums away. I have a baby pivot TT with a brunt alarm and they both works happily...
Alot of people already mentioned about the legality about it, just depends on which officer that you get pulled over.
On the automatic/non automatic part.. I assume you are referring to TT that can sense how hard you have been driving the car and adjust the timer accordingly instead of ones where you set a time.. Again The apexi one you need another plug in (or whatever you call it) wouldnt get it.. the pivot one rocks.. it lets you set two normal non-auto timer (mine is set to 5 min and 10 min.. I use the 10min one to warm the car) and the auto part (I use this normally when driving).
If you have a turbo, I would recommend you to get a turbo timer, as a health thing for your turbo. Remember a few things....
1) make sure the handbrake part is hooked up (what this does is, if the turbo timer is counting down and handbrake is released the turbo timer shuts off, good as an anti theft)
2) if you have an alarm, make sure you ask the alarm installer on what turbo timer they would recommend that would work/compatible with your alarm
A good one is when you can lock the door while the turbo timer is running, an alarm that has a build in turbo timer or an alarm that is dual staged like the nemesis.
Just me 10c worth..