I have the Viper 5901 on my 2010 WRX. It's awesome to say the least.
You definitely want to get it professionally installed though, and even then make sure it's done right. I purchased my WRX used and the previous owner had it installed.
So I've only had two problems with it, and it's not Vipers fault, but the installer. First they didn't get the aux. right for the trunk, so I have to open the trunk from inside manually. Not a big deal.
2nd, and this is the important part. My WRX is of course a manual. And the Viper has auto start. Which is cool and all, useful in the winter. But when installed it has some safety that installes to the clutch??? This is where I'm uncertain, but it keeps the auto start from being activated when the car is in gear. Guess what....mine wasn't done right, and it will start in first gear....
I usually just use the parking break on flat surfaces, but on any incline I put it in first. I was at the beach with my car parked 6 ft from the truck, perpendicular to it. Unlocked the car was getting trash out when it activated in my pocket!!! (this is hard to do anyways but possible).the Car started to take off by itself. Luckily I was where I could jump in and stop it nearly 12 inches from the truck
Scared the crap out of me lol, and it did it once while I was in it. But the remote can be locked so the buttons wront activate until you manually unlock it. And it's supposed to have a kill switch in the car but I can't find it
Do don't let my horror story deter you from Viper, it's a great system. Just make sure it's done right and you will be fine. I have a lot more confidence in my car being protected with Viper than I would without. It also has many other optional sensors that you can purchase, which would makes it impossible to not set the alarm off.
anyways good luck with your choice. oh, and the 2-way remote is great. it has a learning curve, but very functional and the battery lasts weeks without recharging.