I got one of the cheap brass ones free with my trailer purchase. I've used it about half a dozen times thus far, at various locations, with no problem.
I have no problem with the water pressure in my shower. I don't want to say having one of the more versatile, adjustable ones is overkill or anything, but I haven't seen a need for it yet. Having said that, when one of us is in the shower, we aren't running any additional water.
To the question of where do you put the regulator, I put it between the spigot and the hose. Not sure if that is "correct", but it works for me.
Mike