A lack of focus peaking can be a hindrance under very limited circumstances, but I find the little "Green Hexagon" focus confirmation indicator in the viewfinder to be more than adequate for the vast majority of instances, especially if used with the "Catch in focus" ability, whereby the camera will only make an exposure if the lens is in focus.
My
*ist DS is my "go-to M42 camera" and has an M42-PK adaptor almost permanently installed. It has no focus peaking or LiveView and I don't find this to be an issue