You can use one, and then the other one. For instance, I would start off with the injectable, and then would go over to the oral one. Then start the PCT right after.
I would start with the injectable and then run the oral once you run out of the injectable version. The oral has a very short half life so you can start your PCT right after your cycle.
There are no problems switching between oral and injectable forms of the same drug. It's the same drug after all. Just two different delivery mechanisms.