Hi again Iceywolfie,
What sub species/locality of BTS is it? I know some of them need humidity that would be high enough to harm a bearded dragon long term, but a northern (supposedly) likes damn near the same as a BD and most are in the "Egh, shouldn't be a problem" range.
Honestly, I think it's a really bad idea personally. I don't have a BTS but I am hoping to get one in the next few years - my understanding is that they are usually borrowers that need loose substrate, where as most forms of loose substrate are a risk of impaction for beardies. It also looks like BTS eat a higher % of fruit than beardies do, and I would be a little worried about managing their diets. I guess I wouldn't be too worried about the BTS, but I feel like you'd be risking the beardie's well being quite substantially. Googling this I found
this on a BTS forum, maybe it will help?
My personal opinion kind of boils down to the same feeling I have on co-housing two bearded dragons together... CAN it be done? Sure. If you have a big enough space AND resources AND animals with exactly the right personalities to make it work out alright, AND even then be willing to live with the low-grade risk of something happening between the two or because of improper husbandry to cause one or both of the animals to go down the hill.
The reasons for co-housing as I see it are one of two, which is either financial or wanting to represent a biotope. The first I think is kinda silly and probably won't work out well in the long run, likely resulting in sad animals, possibly sick/injured or dead animals, and having a huge possibility of backfiring and costing you more than housing them separately would. The second... Well, honestly the second is kinda cool.
However, I think to make a good biotope terrarium you probably need to sink every penny into one enclosure for the animals that you would in two separate ones and then some! I'm talking if I were to do this, I'd want to doll up at least a 4 foot by 8 foot floor space (preferably bigger!) and go all out, you know?
Whatever you decide, I'd love to hear more about it, especially if you do co-house successfully. I'm P. skeptical of it working, though.