The vertical mouse thing being "ergonomic" is nonsense. There are studies that have shown this. From memory it was generally worse for you to use a vertical mouse in terms of productivity and comfort.

The only thing vertical mice reduce is wrist movement.

Perhaps you might appreciate a different perspective. Broadly speaking, ergonomic devices are meant to combat repetitive strain injuries. I think of ergo devices as useful if they give you more variation. They might not be better positions in themselves, but switching between palms down and palms sideways when moving from the keyboard to mouse gives you variation that helps to combat RSI. At the very least, I couldn't put my palm down without pain for a while, so a sideways mouse is better at least from that vantage point.