yeah I've got a Viper 791. I've found it to be great. I had my installer put in an extra two immobiliser points, plus a remote kill switch...
I dont know how helpful this will be for insurance purposes, although its bound to slow the pros down for at least another 30 seconds!
The remote start feature is the best thing about it for me.. The amount of damage I'm saving on the engine is not calculable, but surely good in the long run. That marketing campaign a few years back for an oil company said that a majority of engine damage is done when the engine is cold. Anyway thats just a perk.
If I had my choice again, I'd have a very difficult decision - although I'd probably end up with the M80 for security purposes. People cant say that their Viper alarm is great because their car hasnt been stolen! It's not until you lose your car that you will change your mind! haha
The remote start and auto window winding is awesome, although window winding can be implemented into most alarms i think?
Conclusion:
Buy the Viper for - Remote start, Flashy remote, 2 Way paging (only if its parked in your garage or within a few hundred metres- sif you aint gonna hear the exhaust anyway!!), engine saving ability if you religiously use the remote start to warm your engine
Buy the M80 for - Security - Black Wiring = harder to steal, Insurance approved (check the viper with your insurance company tho), possibly cheaper, easier to find replacement parts