Dogbox refers to the engagement, it doesn't use synchromesh hubs to get both gears to the same speed before the hub engages the gears. The gears are castellated which mesh into corresponding castlations in the other gears. The use of straight cut gears is for differeing reasons, to cut helical gears uses much more expensive gear cutting equipment plus as already said helical gears impose a side loading on cases & bearings. The advantage of helical gears is they run quieter than straight cut.