Disregard this if you know more than I do, which is probably the case :), but if you are using a 2 part water base epoxy you shouldn't need a primer. I've been told it actually impairs the integrity of the job. The epoxy wants to fill/fit into all the "pores" created by your de-surfacing and...
I have done a few floors using sealcrete and every time I further the process of preping. That desurfacer looks like it did such a good job. They don't have any of those to rent in my city. I used a Diambrush, which did ok but didn't remove material like your unit. Back to your question, I...