So what is the consensus on Bite Fire Blast Tyranitar?

As always, wait for the gym rework...

That being said, I would ask, would you actually use two Tyranitars? It's kind of like Dragonites, I only really ever use one.

As an attacker, it is elite, even with fire blast, but fire blast is still inferior to the other two charge moves. If it were me, I would max out the bite/crunch one and just roll with one big Tyranitar. But if you really want another attacker, I don't see an issue with bringing it to 30.

Usable offensively but absolutely terrible on defense.

I have one and use it for prestiging and low CP enemy gyms. I thought it would be terrible, because its his worst chargemove,but its good. I would power mine up if it wasn't for the lack of candy, the gym rework and the long time fireblast take.
Have also a Dragonite with hyperbeam and the same issue as with fireblast, its already not a STAB move and its takes way to long. Would rather have something like a hydropump or thunder.

I say wait until the gym rework before you make a choice one way or the other. You already have a level 31 Bite/Crunch Tyranitar + other good attackers. Maybe if it were Bite/Stone Edge, or if the Bite/Fire Blast were your only one, I'd say go for it. But since you have options, there's no reason to not wait a few more days when you'll have more information about the gym rework.

I powered my B/FB up to L30 after getting 3 Iron Tail Tyranitars in a row and don't regret it. I'm sure Stone Edge would perform much better but it does just fine against neutral targets.

I have a 96% iron tail/ fire blast that's still at level 20. I'm waiting till after the gym rework to evolve another one

Offensively, B/FB is far inferior to B/SE, but it still has uses. It's roughly as good as B/C against Blissey and the best moveset against a SB Exeguttor. That said, things may change quite a bit next week, with the gym rework.