When used with a chest strap and the Petzl Ascension or Basic, the CROLL makes for a simple and efficient system for ascending fixed lines. The angled attachment hole keeps the device properly aligned on the chest.
I have been using this as part of a frog and rope-walker (used on the right foot) climbing systems for caving for about a year. I use the Croll in conjunction with the Petzl Torse chest harness and have no complaints. The Croll does what is was designed to do and it does it well. The only note-worthy issues is to make sure your Torse strap or any webbing or such in the vicinity of the Croll be neatly tucked away because if webbing gets jammed in the cam with the rope while climbing you'll be there a few minutes trying to correct the situation.
i use my croll for caving doing frog ascension (what it's designed for) and it's the best chest ascender i've seen. never had any problems with it not catching, jamming, or anything like that. i've got a ascension and pantin that i use it with.