Another Happy MK iv user here. I was kind of leery, due to the high price but it beats everything out there for usage. It's programmable for dryfiring, and range practice. Has a Chrony and ballistics computer built-in. It is a extremely multipurpose tool!!
PS At many of the matches another brand of timer will break/not work so I whip my MK iv out so we can keep shooting and not fuss with a cheap timer.