I got a free sample of the OTTO tuning system a few months ago and I finally got around to trying it out. In short, it's pretty cool but it's not really for me - and thus I can't speak for how well it works.
The tool involves two hard plastic gauges and a phone app. Set-up, what little there is, takes only a few minutes and then you're quickly using it. I got through the check portion rather quickly - though holding the camera to see the targets can be a bit frustrating as the app tries to see them just right and keeps telling you to "Show me the targets." [I'm trying to!] But for me, the part where I try to make the adjustments quickly got intimidating - even with all the videos and support. When I made the first adjustment it told me it didn't see anything happen and told me to do a more complicated adjustment. I don't do a lot of repairs and tuning, so when it told me to prepare to dis-assemble my barrel nut (or whatever) I balked. Which probably explains why I kept putting off trying it for so long.
But having a tool that can guide you toward a precision adjustment - and work as a second opinion on the correct settings - could be a great aide to someone more comfortable with such work. And the mathematics of how it works is pretty fascinating.
So, if you're a little more used to adjusting your drive train and more comfortable with this kind of work, I could see the OTTO being a great tool (assuming that it works) but it may not be for idiots like me. I may not be able to give it to someone else, because the app requires a unique code, but if you'd like to try it - and let us know if it works, email me at email@example.com and I'll try to get it to you.