I don't use mtx fluid in my atx, however I don't use the over-the-counter regular shit either. I use this:
https://www.amsoil.com/storefront/art.aspx
I've only ran this for approximately 5-6,000 miles since the last fluid and filter change. I've done a LOT of in-city driving and even went through the mountains to the RMG that reached a 6-7k elevation change in some areas and so far no issues.