There's a method to their madness, as the Grand Tour will be shot from different places, ostensibly from a tent according to Jeremy Clarkson's latest tweet. So they will be touring around the country, maybe even the world, instead of being broadcast from an airfield hangar as during their TG years. This might mean there's no "home" track to test on. We're okay if they leave that bit to Top Gear.
The new Amazon Prime series will debut in August, and the chaps have been busy filming new material for their BBC Top Gear competitor. It will be interesting to see which will fare better, after months of juicy tidbits leaking from the production of both series. No matter what happens, there will surely be lots of burnt rubber and shouting available whichever you end up watching.