Questions for the painters...

I have used a lot of TCP Globa's products and never an issue. But I am always trying to learn of any pitfall that can bit me on my *** as I have mixed products from various companies, which many will say don't do. So here I ask some basic questions for my info and others too.
TCP has a primer called DTM ( dire t to metal). I wonder is that an etch primer?? They refer to it as an epoxy also.
I have also applied their DTM epoxy primer and polyester primers directly over it with no problem.

One thing I have read or been told, is problems that can arise from primers with an acid as part of their chemistry. I (assume?) that self etch primer is an example?? They further state, such can cause a problem with material applied over that.
I have seen a problem with cleaning metal with Ospho ( phosphoric aid solution) and coming back with an enamel. It would wrinkle in places, but I cold hardly DA off the stuff!! To be safe, the Ospho nneds to be reapplied wet, and neutralized with water. Ospho not neutralized can cause a problem with Southern Poly primers they also told me.

Back years ago I used the PPG DP stuff where I had a bodyman do the work I am sensitive to stuff and I can not even satnd to smell it. Great stuff, pricy but good stuff! I have had to do all my own work for decade so I try to use products more friendly to me and less expensive too.