This app was mentioned in 2 comments, with an average of 1.50 upvotes
How is this any different from something like this? https://boxingtimer.org/ https://play.google.com/store/apps/details?id=com.brucemax.boxintervals
Apps look very similar as well. Plus, it seems you have a monthly charge of $3, where this one is a single purchase of $3.
Not sure that a boxing timer warrants a subscription.