Not a fan
A few years ago a collegue had a problem with his wrist so the company bought him one of these in a lovely shade on beige. I had a go and found it a bit too weird - I don't know if I'm using a mouse like a knacker but the mouse pointer moved slightly up as well as I moved the mouse to the left. Also you had to hold it in one position where as I use my mouse in whatever position I grab it (no pun intended).