Being a person that sells a servo kit, I may seem biased, but they are pretty cool. I have an older FP helmet and with the servo installed, I can't get the helmet over my big melon. I plan on getting a new helmet down the road and hopefully the new helmet will have a bit more room inside. I am still working on a bracket for the servo that will allow for the removal and reinstall of the servo ( i have a prototype of the bracket in my helmet). I think the hardest part of the servo kit install is figuring out the best way to attach the stalk to the servo. With an aluminum stalk, its easier since you cna drill and tap a hole and use a set screw to hold the stalk in place, but there isn't a steady supplier of aluminum stalks (especially hollow ones).
I plan on making my servo kits an ongoing run, but I am also trying to find ways to improve it as well to make the installation as easy as possible.