Dtm primer question.

Hey guys I'm getting ready to order my primer and paint I have a some questions about the primer.
The primer is a 2k high build urathane dtm primer it's got the etching step all ready in it to save time and money. The other 2k primers says it can me sprayed over properly prepared substrates (etched primered steel) other primers and OEM paint etc. The dtm says can be sprayed on bare steel and other prepped surfaces. So does this mean I have to go all the way to bare metal? Or does it just not include it like the others? And yes I know it's best to do it in steps and do the etching primer and epoxy primer and the build primer to block it I just cant afford to buy three different primers. Also has anyone used the regular 2k urathane high build primer on bare metal and had trouble with it sticking? Should I pay extra for the dtm? Iv read the dtm doesn't block as well as the regular old 2k high build. Thanks for your help