In the past, Boston-based Whoop has said existing subscribers of at least six months would get new hardware for free and that new software features would come to existing users.

There was plenty of vitriol directed towards Whoop over on Reddit and social media, from users who expected to get the new bands for free within their current subscription. That's now the case again, after Whoop decided to reverse course.

Consumers are lashing out at fitness technology company Whoop after it backtracked on promises of a free upgrade.Whoop marketed itself and its fitness trackers with a fairly unique subscription model.