Pros: Unified wireless. On/Off switch on the base. Internal storage for extra Unified dongle means you can grab it from your desktop and and have a mouse to use on your laptop on the go.

Side buttons and mouse wheel tilt actions are configurable. Other buttons are not.

Scroll wheel has nice action. There's a slight detent when it turns. (I hate when it spins freely with no action that you can feel.)

Buttons have nice action.

Cons: Tracking. It's absolutely terrible at tracking surfaces. I have three other (much older) Logitech laser mice to compare to. The other mice work on every surface I throw at them except for a black wood surface that has very rough wood grain. The M510 only works on one surface I've found so far, and that is a brown faux-leather cover for a pad of paper.

Surfaces the M510 cannot track on, but the V450, S520, and three other corded laser and optical mice track perfectly:

* The fabric arm of the couch.
* The pleather arm of another couch.
* The very slightly glossy granite table, only -barely- reflective, with lots of fine matte stone patterns underneath a very thin very subtle gloss.

It CAN track on:
* The thick, uncomfortable binder cover.
* Pant leg.
* A piece of paper. (But the paper moves. And if I have to duct-tape paper to my table to use my mouse, something's wrong!)

The biggest issue is the table, since the whole point of having the more expensive laser technology is to be able to use the mouse on the table without having to confine yourself to a mouse pad or other specific surface.

This is not the driver issue reported by some others. I searched after buying this mouse, and lots of people are reporting the same kind of problems. The M510's laser optics look different from all the other laser mice, so it looks like simply a bad design that looked good on paper but doesn't work in real life.

Also: Side buttons in games. If I assign them an in-game action, the settings screen reads the mouse event just fine and assigns it something that looks reasonable. But when I try to use the button in game, only one out of 10 tries actually causes the action to happen. For example, in Deus Ex: Human Revolution, if I assign one of the side buttons to "throw" and the other to "enter cover", I can press 'throw' seven times on average before he actually throws something. The same with 'cover'. Assigned to the middle mouse button or a keyboard key, the action happens immediately 100% of the time, on the first press.

Also: Resolution. If I turn the sensitivity up enough that my usual 2-inch range of mouse motion covers more than half the screen area, the mouse starts to skip over some pixels two at a time. I hate mouse acceleration, but the only way to be able to reliably be able to place the mouse at an exact pixel (e.g. for Photoshop) is to have acceleration enabled.

Also: Not a big fan of the texture of the rubber. It feels tacky, like it's already (after three weeks or so) starting to absorb oils.

Other Thoughts: The Unifying drivers seem to be able to configure other Logitech mice, even when they are not 'Unifying' mice. For example, the V450 shows up and for some reason has the middle mouse button configured to 'document flip' instead of middle mouse click. (Naturally, this can be set back, it just seemed interesting.)