I have had my first MX vertical mouse since April 26th of this year. This week the top (left click) button stopped working, requiring multiple presses to work. I used a pressurized air cleaner in case there was dust, and that did not work. I lightly spayed 99% alcohol and no improvement. I bought another at over $90 from Amazon as I like the mouse... a lot... but less than 6 month's service life on the switch is not acceptable.