What is the best presidium model?

I have the colored stone estimator model and like it very well. The duo meter is good for follow-up testing of colored stones,also. The main thing to remember is that you have to make several tests to verify a gemstone properly, such as a refractometer, etc. Presidium is top of the line.

is there one now with a moissanite tester?

Yes that will the presidium duo model we have it available starting at 349

The red light won't stop flashing to indicate the tester is ready for calibration. What can I try to reset it?

As you stated, the Tester is ready for calibration. Please follow the calibration instructions in the little manual or go to the Presidium website. Good Luck!!!