I've been using a Logitech M570 thumb trackball at work for about a year and a half now. I like it quite a bit. It would probably be perfect if it were a couple millimeters longer and wider.
I got the M570 for $26 on Amazon. Walmart.com also had them for this price, but, in store, they were $40. Now the price seems to vary quite a bit, but nowhere has them as cheap now. I'm wondering if I should try to grab another one or two for the future when they are still available or if I should just try out the Mx Ergo. It's still over double the worst price of an M570.
Does anyone personally know how they compare in shape and feel and size? The tilt is appealing, but the forward and back buttons' flatness is concerning. I'd be happy if it's bigger (or feels bigger in hand) than the M570.