If you're going to train by MAF, you'll either need a watch with an optical HR monitor or a chest strap HR monitor that connects to a watch.
I have the Garmin Instinct and really like it. It’s less than $200, although, there is a solar-powered version one now that’s $400. Garmin makes many different styles of watches if you want something less sporty and more every day.
The Coros Pace 2 is super light, has an optical HR monitor and is packed with features for about $200. Here is a review from the Ginger Runner.
If you want something more high-end, you can also check out the Coros Apex. Here is a review from the Ginger Runner. Ginger Runner Coros Apex review
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