If you give Ennis 3 guaranteed months to show how good he can be, you surely have to do the same with others on the fringes - Randell, Law, arguably even Burton. 3 months in the team could give confidence, but can also bring complacency.
There needs to be competition for all places. The difficulty is as to how a player competes for a place when not in the team. A couple of reserve team hat tricks might show that Ennis, for example, is ready to start, but we have no serious competitive football for those just outside the first team - something that is hurting us in several ways.