I've heard that style called the "Russian" type and I've heard that it's one of the worst type of the clutch handles to use, I dont know this from experience just what I've read multiple times.
Thats Dax has the locking handles Page Title
, BGF on ebay has what I think are the best ones I've used, they have a longer handle so they are easier to pull than the little short handle ones.
This is the best one I've used so far.... link below
bicycle Motorized GAS motor - clutch lever long handle | eBay