Simple to use, whole phone changes color red <--> green for active/recovery periods, so can tell instantly what phase I'm in. Makes it clear whether I should be running or walking. Good for protocol adherence.
why only limit set to 9 Simple and easy to use, why limit set to maximum to nine (9). Would rate higher if developer can update allowing user to chose higher set.
Professional High-intensity interval training For Boxing, Circuit, HIIT, Tabata