Since I am "professionally frequent clickers", I had for some time severe difficulties with the tendon in the right forearm. This vertical mouse is still one of the cheaper, I have found me to try out. I will not give it back - since I, the tendon pain are passé. However, it has some familiarization time needed! First is uncomfortable that the hand bones outside very much "seated", carrying practically alone all the weight of the hand. That's what I have, however, become accustomed to two or three weeks and am now completely free from pain. However, my elbow is also on the armrest of the chair desk - who has an attitude without arm support, so that will not be so lucky. The "front and back" buttons are on the left side of the mouse is not very well positioned, it is a bit tedious to get there with your thumb off, I use them rarely. Otherwise, the mouse is very well for me in my hand - I have pretty big hands for a woman. However, I will scroll with his forefinger. If I try to scroll with the middle finger, the attitude is a bit uncomfortable. So you should weigh all the "trappings" before buying.
