Actually, I wanna put my opinion on this.
I assume you will want your Garchomp to hold the Garchompite, no?
Well, you can't hold two items at the same time. So, why don't you keep the Garchompite on the Garchomp, while also using Hone Claws?
I mean, Mega Garchomp is quite bulky therefore you should have enough time to hone them' claws before doing a Dragon Rush. Plus, Hone Claws will also boost it's already huge Attack stat. Dragon Rush will definitely be a big move on your moveset.
So, I would recommend getting TM01 onto your Garchomp.
Hope I helped. :)