I use Gm with TT all the time, as I like the way you can drag your route where you want with GM.
However after I download it to my TT I then open it with Tyre and delete a bunch of W/P in between curtail turns.
Then I save it to my TT and when I go to use it I turn off my IQ routing other wise TT will take me on what it thinks is the shortest route and that may differ from where I want to go.
I find it works great for me but that is just my opinion.