I have installed the Mid City Smartkey starter in three vehicles now. It's a 2 difficulty on a scale of 1-10. The last time I did it, it took 10 minutes! My wife's cars has their newer "Next Generation" version (NG in the part number) which is very slick. Even turns on the seat warmers for her in winter. Mine is the older unit without that feature.
The best thing about Mid City is if you call them you can talk with the guy who invented it, Dan Ruby. He is a nice and very helpful guy! He told me some helpful tips for those looking a great deal. There are actually only three models of the original Smart Key Starter units depending on the speed/type of CAN buss in the vehicle. They are referred as SKS-FT "Fault Tolerant", SKS-HS "High Speed" and SKS-CHS "Custom High Speed" which is rarely used. The only reason for the dozens of part numbers on their website is for the different wiring harnesses, which you can buy separately. So, if you see a used unit on ebay for some random Mercedes model and the price is right, it will work in your car if the CAN buss type is the same (FT, HS, CHS). You just need to order a different wiring harness for $99.
The NG models are even easier as they have made them universal with all the necessary ports (Drone, Directed/Viper Smart Star, D2D, Keyboxes, Antennas, etc). Even firmware upgradeable!
Nice man . I have the latest version on my glk which initiates them at different outside temperatures but what sucks is that in Mercedes they only activate when you sit on the actual seat . My wife bought a 19 Q5 prestige and I wish they offered same plug and play starter for Audi but I don’t think they do .