Ditto what else has been said here about bra & HRM strap fit, etc. And, the Nike sounds great.

But, I am one of those who has a Polar that was about $70, and I wear the strap for long rides...up to 10 hours, etc, and have no discomfort. I wear it with a sports bra (no underwire). Don't even recall the brand of bra, and I will be shopping for a new one soon, just because it is time.

The watch is ugly, and way too big for my wrist, but I don't care, because I mount the watch on my bars, which I find easy to monitor and use while riding.