Using the Trust system will teach you a fair bit, though a lot of the difficulty in tanking can be dealing with other players and adjusting accordingly. I think it's certainly fine to start out using the Trust system, getting used to how the job plays, figuring out when to use what CD, etc. but the way I'd personally tackle it is running the dungeon once or twice with Trusts and then running it with actual players. If you're in an FC (LS works too), I'd try and find some buddies to come along and help out for the "real" run.