I can't remember to have read a single post on this forum where a member said he owned one or used one.
I have seen only one of these once in a store a couple of years back. Protool version. My first impression was it was very big and heavy, over 60 cm (2 ft) tall. Built very solidly. Spring action was very smooth, and so was the angle adjustment. Not indexed, except for the two outer stops, 90 and 45 degrees. Just move it to one side until you can go no further and you've got 90 degrees, and 45 to the other side.
I have not used it of course, so I don't know how it holds up over time, but considering how solid this was built I doubt it will get sloppy as quickly as the small cheap types.
But it's really big and heavy. Keep in mind it's meant for rough construction, not something you want to use for your typical 'around the house' tasks.