Sometimes something is better because you have it when you need it. I wanted to make cider, my LHBS was an hour-and-a-half drive away, and I didn't feel like waiting for mail order. So I tried using tea, liked the cider I made with it, and kept using it.
I have absolutely no evidence that it's subjectively better than powdered tannin, except conjecture, and I guess that's a kind of evidence.
I keep a lot of tea on hand because I like to drink it, and I keep a lot of oak on hand also. If I can remember next time I'm at the LHBS I'll pick up some tannin powder and try it out. How much per gallon should I start with?