That's a good one. I would say to be safe go with the AMP. The MIC mounting position on the OTTO places it underneath the ear-cup. Again depending on your shooting style and bone structure it may not be the best solution as the MIC mount will ride on the stock not allowing the best sight picture depending.
So there I'll say it OTTO missed the mark on shooting ergonomics a little.
The OTTO is fantastic kit, as well made as any top notch product available but the design ergonomics are lacking if things don't align into place. OTTO reminds of the old Motorola solid built quality. You can feel it just holding it your hands that this is well made stuff. The water proof aspect is another. I think the OTTO is to a higher standard than the AMP but I could be wrong. Who knows they may make some modifications to the OTTO in time but as of now and if you have the extra coin buy once cry once I say go with the AMP all things considered. Now it has been done that people are using the AMP helmet mounts to adapt other headsets so if for what ever reason you decide on the OTTO you might be able to use the AMP helmet arms as I have seen some neat rigging as of late on Peltors , Sordins etc.
Some of this fan boy stuff we use is really not worth what we are paying for, Work, hobby or whatever and Ops Core is going with the traffic so just be ready to pay an additional $200 over the OTTO if you can even find it right now.
Again the sound quality of both are super.
OTTO = basic range work tough as nails
AMP = high speed down range operator who may need the edge. Helmet mounting is a big plus.
At my age I need all the help I can get ............
I hope I've been able to give you some non-professional insight but at the end of the day it's what ever fits you best and what you want to invest.