Agree to all 3 of the above with some modifiers.

1. Many folks don't bother to use HR on endurance rides. I did two almost back to back 200 mile + rides earlier this year and used the chest strap for one and nothing for the other. The chest strap double C pointed out what I already knew. I was loafing along at a sustainable for evar rate of 120 HR. (It doubles as a blinky in a pinch too. The 3 rapidly flashing LEDs can be seen from a good distance.

2. Tuck under jersey sleeve with strap or without. I have used my Schoche Rhythm with and without the strap under some of my tighter jerseys. (I have arms that belong to humans not "cyclists" and a jersey that fits the waist tends to be a bit snug in the arms, YMMV) Tucked under the sleeve right above the gripper is 100% pure comfort but I sometimes worried about it falling out even with it being snug and seemingly shake proof.

3. Paid 79.95 free shipping no tax. Close enough to $100 considering that is 2X chest straps. For some that is "Meh" money if it works well. for me getting kitted up and then thinking about the HR strap was a common occurrence. Slipping on an arm band after getting ready to ride = priceless.