Toyota dealers in my city outsource remote starts to 3rd party installers (non Toyota remote start systems). It's a known fact they are tapping into wires and soldering, etc. No mention of voiding warranty, especially since the Toyota dealers are the ones outsourcing the work.
Installing can take a long time, especially if you are first timer. You have to know your wiring on your car, and wiring coming from the remote start module, by-pass module, etc. My installer friend did mine in 1.5 hours, but he is a pro and knows all the wiring for different cars in his head. A newbie could take a full day and if you screw something up, be prepared for a lot of troubleshooting.
I have a Compustar Pro Remote Start installed on my 07. The main benefit over OEM is range.
2007 RAV4 Limited V6 4WD 7-Passenger