I'm no expert on TS providers, and I'll go on the record by saying that I have no interest in venturing forth into that side of the hobby.
However, I will say that not all TS are 100% gay. Some are actually known to have sex with biological women as well as other men. Call it what you want, but that is bi-sexual.
Now, here's a hypothetical situation.
What if one of you chest beating heteros out there has an ATF that took part in a session for mucho dinero...that involved a TS? What if she got fucked in every orifice in her body by another man, the only thing is...he has bigger bolt-ons than she has, and happens to wear lipstick and high heels?
Here's the kicker... She doesn't bother to tell you or anybody else for that matter, because it isn't any of your fricken business. So...you see her because she's your ATF but you have no clue that she just got pounded two hours earlier...
....by a TS with a bigger cock than yours.
...and you have no clue because why would she feel the need to tell...you? Who are you...someone special that needs to be informed of every sex partner she chooses to see? Get over yourself.
This hobby is full of risks. Accept it, or take up crochet.
My .02 on the matter.