As much as I like the idea and would love to use it, but I am not really motivated by the fact that you are taking the money, you are not offering any service, just using people's procrastination to make money, I don't know about others but I really don't like that.

It could be much better if the user has to choose a charity that money goes to, I understand that you also have costs for running this app, but I think I will write my own app and besides that, it's not always about workouts, it might be about reading , FOSS, self development, or whatever of that things, would love if it had something like that.