I've got a Logitech R800 too, and it's pretty much perfect. The timer is great when I'm doing training, as I can set it to the time between start and breaks, and just run through. Has little vibrations in your hand to let you know you're running out of time.
AAA batteries can just be swapped out, it's pretty great.
I'm really keen on the new Logitech Bluetooth one, but it doesn't have the timer screen, which is a real shame. I've noticed recently sometimes I can't get line of sight to the R800 receiver, and I've got a new MBP w/touch bar, so using a USB-USB-C adaptor to connect the R800 receiver is kind of dumb. If the new Logitech one was $50 cheaper and had a timer screen, I would have bought it already.