The MX Vertical looks like one of Logitech's modern mice flipped to its side, sitting atop a melted puddle of wax. It's unusual, for sure. But that design has a purpose. As your hand approaches it, your wrist turns slightly to fit into the thumb groove. Your fingers rest on the top buttons in a natural way. And your arm straightens out, so that you're not just controlling the mouse with the force of your wrist. Logitech calls the 57-degree angle of the MX Vertical a "natural handshake" orientation — holding it is almost effortless.
I've used Logitech mice since hopping on my first PC in the mid-90s, and I've tried a variety of experimental mouse designs with varying degrees of success. But any hesitation I had about using the MX Vertical melted away the first time I held it. My hand landed on it perfectly, and while it took a few minutes to get used to its unusual orientation, I was eventually zipping around the screen as accurately as with my usual mouse (a Logitech MX Master).
It handled most productivity work, like browsing through web pages, scrolling through documents and sifting through emails, without any trouble. The MX Vertical is also useful for slow strategy games like Civilization VI, but unfortunately, it's a bit too slow to move around quickly for fast-paced shooters. (That's not a huge surprise.)