I would get the less expensive set. It will serve you just fine.

The EPA Test can be taken for $15.00 at www.imaca.org

You are wise for buying R12 gauges for R12 and R134 gauges for R134. Mixing the refrigerant itself is not really a problem, but you should try not to mix the oils. Mineral oil works great in R12 systems and is cheap. That way your R12 gauges will never see anything except 12 and mineral oil and you R12 systems will have no doubt of being contaminated in any way except the possibility of moisture if you don't evacuate properly.

Good luck,