Occasionally I teach a climbing class, so I purchased a cmi foot ascender for students to use, because the pantin I have does pop off the rope when students use it. The locking feature does stop the rope from coming out, but also complictes removal from the rope. When you draw your knee to your chest to release the cam there must be zero rope pressure on the ascender or the cam won't open. The pantin takes a little getting used to but you can take it on and off with no hands. There is a hole in the ascnder shell if you want to lock the pantin to the rope you can use a mini ****** behind the cam until you reach your destination. The cmi is built like a brick, in my opinion it is overbuilt for its purpose. It is not used for life support. The pantin is more streamlined and is less cumbersome. Just my 2 cents.
Corey
P.S. Cmi ultra ascender is the best handled ascender made, while Petzl handles are only marginal.