A heart rate monitor is definitely worth the investment, and I've heard you can get some good ones for around $60 from Polar. Using one is in my opinion far superior to using the fitness tracker, because the tracker can't account for individual differences and fitness levels. Especially something like HIIT.
"I have a personal relationship with food. I love it, but it's on the fence about me." ~Kathy Griffin
"If there was a famine, we'd be the last to survive." ~My mother
| current weight: 137.8