Hi Rich,
I bought an R-Tech AC/DC machine (UK brand similar to a number of other machines) about 2 years ago because I could not trust my old Machine Mart MIG for some more highly stressed work (and I was curious about TIG). I have had no problems with it and it has stood up to my learning on it. (No relation just a customer)
Once I got the hang of TIG, not like the YouTube pundits but good solid welds repeatedly, I did think of selling my MIG and just doing TIG. But then there was a too good to miss offer on an Esab MIG and I went for it. The Esab is a completely different game to the Machine Mart MIG and has made me see the virtues of MIG again (quick, less prep, less and cheaper gas). Now I pick between them based on the job.
I did look for a combo machine back when I was looking to TIG but there was not much out there that also had hf start (which I considered a must). I do not know why, most of the parts would be the same, plus the spool mechanism.
All the best,
Martin.