I'm bringing this back for an update. I bought the Emay device for Windows from Amazon. It's easy to use, but (as was suggested) it is sensitive to how it's held, and it gives funky readings if I move around during the scan interval (which I have set to 15 seconds). As I use it more, the readings are becoming better as I have learned how to hold it without inducing movement errors.
It turned out to be a blessing because my cardiologist's office isn't doing face-to-face office visits these days, due to the COVID-19. My six-month follow-up today was a telephone appointment. Thanks to the portable EKG, an automated blood pressure machine I have from the VA hospital, and a personal pulse oximeter (also from Amazon), I was able to e-mail complete vital signs and an EKG printout to the doctor for him to look at when we spoke.
He was VERY pleased with the EKG. Not just that mine didn't show any problems, but also with the fact that this little toy actually produces useful results. He said the readout was properly formatted and he was able to read it without any hiccups. Had there been a problem, I guess the next step would have been to have me come in for a real 12-lead ECG, but for routine follow-ups this device seems to be more than good enough.
I'm glad I bought it.