I tried the third party grip path as well, on a 60D refurb. It worked for a year then started draining both batteries overnight. I decided at that point to save the aggravation and just buy the Canon grips. They fit better, feel better, work better and longer. I know they are expensive, but in the end, I find the value worth it.
I just picked up a 5Dc and it came with a third party grip. When my used RRS bracket showed up, it didn't even fit because the dimensions of the third party grip are not exactly the same as the Canon grip. I bought a used Canon grip and the L bracket fits perfectly.
As always, your mileage may vary.