My cheapy ones arrived yesterday didn't get round o putting them on as I went out for a ride instead, is there a correct angle to have the flat bit for the palm or is it trial & error?
I am in the same situation.
The correct angle is the one that feels most comfortable to you!
My MTB is currently out of action, awaiting brake repairs, but I have been playing about with the palm rests, holding them at different angles. Some are definitely more comfortable than others, and are much better than my old grips.
A good starting point is one that lets you grip the bars with your hands directly in line with your arms so there is no bend at the wrists. Angle the rests so they support your palms there. Adjust the angle of your controls so they can be operated without having to bend your wrists away from that position.
I will set the angle of the little bar ends using similar thinking. In my experience, bent wrists on long rides are not a good thing.
I am quite impressed with the appearance and feel of this product, but I do wonder how well the bar ends will cope with crash impacts. My old bar ends are heavy duty aluminium, stronger than the bars that they attach to!