I have had an issue with my original HR strap on my Garmin 300. I would get spikes at the strangest times. This concerned me because I do have heart issues and tracking my HR is vital to me. I upgraded to the new strap and believe that it tracks my HR much more accurately. I share your concern for an honest count.

The finger and watch method is always best. BUT, I once took a tumble trying to pay too much attention to my monitor while riding. I prefer to focus on the ride in front of me. If you get to a stopping point and can take a 30 second break for a count, that is the most reliable way. In my mind, I can see that I can set up a screen on my Garmin with a clock with seconds. I can take a count in a safe stretch of trail.

I have been posting here for a few years. The people responding here are reliable. I don't think anyone is being sarcastic. I am comfortable with me being a middle of the pack rider. I am 60. Some of these guys have decades of experience and take for granted what they can do on a bike. I enjoy their skills and knowledge. I am not that coordinated.