I am not worried about the ill effect, more if it's required in the winter to get the temperature up.
For 70$, the more I think about it, the more I might go without. I will try it without and if I notice it's too hard to warm up the transmission in the winter, then put the control valve. I will put on a temp gauge though, this will really tell me how the temperature is affected.
I bought a camping trailer, so I know I need the transmission cooler, but I decided not to spend the money on the control valve unless I see I need it, since it's easy to add after the fact.