Others here likely have more experience than me but I’ll come out of hiding and admit I’m doing both (on my 6th week of 6mg Reta + now going into my 2nd week of 1mg Tesa) and have had no issues.
I’ll be getting some more baseline bloodwork done soon (mostly for check test, tsh, and igf1 trend), but supposedly the thing to monitor would be your fasting glucose and HbA1c levels across multiple readings as a trend as indicators that the two combined may be an issue.
Anecdotally, I started doing both myself out of a desire to more quickly manage my visceral fat and to help avoid loss of muscle from reta alone.
I’ve been measuring and monitoring my waistline, knowing that Tesa water retention will stall and hide reta weight loss occasionally and I’ve already reduced by an inch in the week after starting Tesa (caveat here is it could have also been reta momentum as I’ve lost close to 2-3” of waistline overall including this most recent loss).
In that case assuming you don’t have other complications like diabetes, etc. I would think that any cons for combining both are outweighed by the benefits; but if you have reservations you can’t go wrong with just sticking with Reta. Reta affects both sub-q and visceral fat, while Tesa primarily affects visceral fat.
. 
