Try looking at it from a different perspective. If you like your Prima Dia II, consider adding the inboard MM phonostage ($200) and be done with it. That is two less connections in the signal chain. You will also be getting a better power source which is an additional upgrade (separate power suppy) on budget outboards that offer it. I'm not a big fan of outboards that offer MM & MC. When a component offers more than one feature (a receiver, for example), compromises have to be made. That said, if your a fan of "ole silver face" and believe there hasn't been any improvements in audio technology in the last 30+ years, then a sub $200 outboard MM/MC will do fine. I have owned a handful of them and one might do one thing a little better than another. But, it's more of a matter of taste in the end. People who respond (and are honestly trying to help) have not heard your gear together in your listening area.
If your determined to go outboard, there are a few I like better than others, but we probably wouldn't reach for the same thing to drink from the refrigerator.