The Logitech M510 replaced a Microsoft Intellimouse Explorer 2.0 with a left button gone intermittent. I was looking for something with similar heft, basic wireless functionality, and reliability. The M510 is a pleasure to use, but be aware that you cannot make application-specific assignments to the buttons and wheel. (In the screenshot of the Options software for the M510, note that the "Application Specific" option normally found top right is missing.)GOOD CHOICE AS SIBLING MOUSE TO OTHER LOGITECH DEVICES:A good experience with the M325 travel mouse combined with Logitech's solid Unifying Receiver technology led me to the M510. The unifying receiver works alongside Bluetooth but without the driver and performance problems faced with Bluetooth 2.0, 3.0, and 4.0 on laptops and desktops ranging in age from 2007 to 2015. Logitech allows up to six devices per receiver. For a laptop that spends some of its time on the main desk, some at a standing desk, and some at coffee shops and client sites, the ability to fire up either mouse and have it work is one task when changing work locations.SIZE, SHAPE, MASS:Ergonomically, the M510 is a standard size mouse, slightly narrower and shorter than the old Intellimouse. One worry that failed to materialize was the loss of right-handed asymmetry, which I don't miss at all. I rarely use auxiliary mouse buttons, and the two slim left-side buttons--the only concession to right-handedness of most consumers--I customized via Logitech Options software (oddly, a separate component from the Setpoint software required to customize the M325) to Volume Up/Down, useful as replacements for the difficult-to-find volume meta-key controls my particular laptop (HP 640).My regular use of an M325 and a mousepad with an elevated wrist cushion has over the years nudged me toward using my upper fingers and fingertips instead of a grip closer to and more in contact with the palm. Only those with small hands or children could use the M325 with a palm grip. The M510 is definitely longer, wider, and heftier, but still smallish for larger hands.With two batteries, the mouse has a nice heft, which can be a nice change from using a lighter travel mouse. The device will operate on one battery if less mass is desired.TRACKING ON SURFACES:The mouse works well on all mousepads and on finished wood. On glass, the performance is touchier and the mouse does not glide as smoothly. Not tested as "couch mouse' on fabric or skin (eew, anyway).I could have continued using just the M325 for all my computer time, but as a telecommuter who spends 50-80 hours per week with database tables and spreadsheets, I like to mix up my work environments by switching among desks, chairs (or no chair, at a standing desk). I do this to ensure I'm not settling into one potentially harmful constant usage pattern. I extend this variety to my choice of keyboard and pointing device. At the risk of sounding like a Logitech shill, I enjoy switching among big mouse (M510), little mouse (M325), and the built-in laptop Synaptics trackpad (and until my most recent laptop update, a pointing stick).WEB SITE:The noteworthy Logitech registration process allows you to enter the serial number, purchase date, vendor, and even allows an upload of the receipt. The warranty expiration date comes up for all devices registered. This feature is appreciated in a world where most of us have dozens of electronic devices with various warranty lengths purchased at different times. I may not always have occasion to test Logitech's customer service, but if I do, I know I can go back to the support site and find my warranty expiration and even have the proof of purchase receipt already in their system (says the world's not-quite-most-interesting reviewer). The receipt upload combined with the live warranty expiration date is one of the better ideas I've seen on any electronic device manufacturer's support site.SOFTWARE SUPPORT (beyond built-in drivers)A minor quibble is that different software packages are required for different mouse products (specifically, SetPoint for the M325 and the overly-generically named "Options" for the M510). Both installed without a hitch in Windows 7 Pro. The M510 works well with the stock Windows driver; install the Logitech software only if you need to change settings not available in the stock control panel.The "Logitech Unifying Sofware" must be installed to register another Logitech device on the same receiver, a quick and simple process.PROs:The click on both left and right is consistent and easy to long-press or double-click.Directional buttons are reasonably convenient, if a little awkward at first. They take a fairly deep stroke, and feel a bit spongy.Two batteries but can operate on one, if a lower mass is preferred.Built-in internal slot to carry Unifying Receiver.Will work with other Logitech devices via Unifying Receiver.No Bluetooth compatibility woes.CONs:Marginally small for those who prefer to whole-hand the mouse.Auxiliary directional buttons might be too awkward, and take a deep press to actuate (listed here again, as for this feature one person's pro might be another's con)Unifying receiver required, which means one USB port is taken. Mouse did work well with the receiver on a hub (Asus PB238Q monitor USB port).No Application Specific settings available in new "Options" software.This mouse (M510) uses "Options" software. M325 uses "SetPoint", which offers more control and is integrated with the WIndows Control Panel. It's a mystery as to why Logitech would choose to dumb down what has been a mouse control panel standard for 20 years, unless they want to force customers to choose a more expensive product. That knocked a star off what would otherwise be a near perfect product.Overall, the M510 is a high quality, reliable device for standard office work and some graphics work (not tested for gaming).