I have been using Garmin bicycle GPS Speedometers for about 5 years on my Classic motorcycles and Vintage cars. First an Edge 200 now an Edge 500. I find it useful for keeping a mileage log and map of where I have been as well as ensuring I keep to the speed limits as some of my vehicles don’t have speedometers or accurate ones. I have yet to discover what happens if I exceed 99.9 mph. I haven’t yet checked Waze against Garmin to see if there is a difference.
“Hello Officer, here is my licence for you to cut up . . .” 
There but for the grace of God 
Please, please don’t try to test it - and certainly not on your bike!
My ND does have autobrake but you can adjust the sensitivity. Mind you last time I was out in it, it didn’t autobrake but I got a beeping sound and “Brake Now” warning on the dash or MZD screen (I can’t remember which). There was absolutely no reason that I could see for it, as I was on a straight bit of road with nothing anywhere near that might have warranted the warning. I don’t need that, I have the wife for that.
I think as well as dumbing down the driver skills requirement Mazda are also trying to make the need for a co-driver (backseat?) redundant as well.