Pros: Wireless, Unifying Receiver, uses two AA batteries, perfect size for my hand, is optical
Cons: Feet wear out quickly, scroll wheel moves a bit too freely
The biggest plusses for the M525 is it's wireless and the Unifying Receiver that lets the mouse talk to the computer. Unifying Receiver is Logitech's name for a receiver that can be used with up to six different compatible devices, such as keyboards and mice. Instead of using up to six USB ports on your computer, all you need is the one receiver. The receiver is also tiny so it doesn't stick out a couple of inches, just waiting to get knocked off. Devices compatible with the Unifying Receiver have a place where one can store an unused Unifying Receiver when using more than one device with one receiver.
The mouse is powered by two AA batteries. Claims for battery life are greatly exaggerated, even if one is religious about turning the mouse off when not in use (like I will remember every time) but, using Sanyo Eneloop prechargeable batteries (they hold their charge much longer than normal rechargebles), I can get several months life out the pair. Changing the batteries is easy. There is an easy to use on/off switch on the bottom of the mouse.
Since this is an optical mouse, there isn't any ball to collect crud that will eventually cause the ball to seize up.
The scroll wheel moves more freely than I (and, I'm sure, most other people) particularly care for. I was able to get used to it, however.
The feet on the mouse I use at my desk (the one that gets the most use) started dragging after about six months of use. I contacted Logitech about getting replacement feet. They replied they don't sell replacement feet but offered to replace the mouse under warranty. I passed on that since I would have had to pay shipping on the return and the mouse I received back would probably wear out its feet in the same amount of time. Instead, I found some Teflon mouse tape (http://www.amazon.com/CS-Hyde-PTFE-Mouse-Color/dp/B003DZ16X4/ref=sr_1_1?ie=UTF8&qid=1387345143&sr=8-1&keywords=mouse+tape) that is fairly easy to apply on top of the original feet and will last for several months, despite being rather thin. When the mouse, with the Teflon tape applied, is used on a hard surfaced mouse pad, the mouse glides across the pad like it was on ice.