What this game trains
Number Hunter presents one target value at a time from the mixed pool your difficulty selects — plain digit runs at the lower levels, and phone-number, ZIP, customer-ID and decimal formats higher up. Your job is to reproduce the target exactly, including any dash or letter prefix it carries.
Reading mixed formats
The interesting difficulty here is switching formats without pausing. Going from a five-digit ZIP straight into a hyphenated phone number forces your hand off the number pad and back, and that transition is where most people lose time.
Practice the non-digit characters separately if they are slowing you down. A dash or a letter prefix keyed hesitantly costs more than three digits keyed quickly.