Fitch is suitable for all pets
You won't use as much for rats as you will gerbils and hamsters as gerbils and hamsters burrow while rats don't need very deep substrate(as you probably already know).It's really good due to it not being able to cause allergic reactions like other substrate,plus it has very little dust if any and would not cause respiratory problems.
I haven't heard of tea bag bedding,but to be honest I'd just go with Fitch.You can get massive amounts(bulk orders are cheaper than just getting the single bale),so you can have the ideal depth for gerbils as well as any size hamster but also make it last a very long time for the most part.