I think simple is best.

Large readout, easy to understand.

Personally, I think most folks use the HRM for a while and then lose interest in regular use of the HRM - except for those few who get really fascinated by this approach.

I ride mostly for fun, and find that too much technical stuff detracts from the enjoyment.

I have a Nashbar simple unit which I got on sale for $49.75 or thereabouts. It works very well, tells me my heart rate and I go from there. All in all, I find that heart rates vary so much from individual to individual that most of us can not use the simple formulas for MHR that you see around.

Have fun.