So I am riding a horse was in a corkscrew but IMO it was way too much bit, so all I could find to switch the horse into was a copper roller I figured it has to be lighter than the corkscrew. Decided to put it on and the horse was wonderful, a whole new horse. I am just interested on what these bits actually do, how harsh they are and what the point of having the rollers on the bit.
The harshness of the bit depends on what type of bit has the copper rollers on it...I've got a couple single-jointed D-ring snaffle copper rollers, as well as the same but in a curb. The copper rollers themselves can provide an outlet for the high-energy extroverted (high energy and always in your face, like the extroverted person, lol) horse who always wants to play and keep his mouth busy (I use the snaffle on my Quarab, who loves it - he is always playing with things with his mouth though and is an extremely high energy horse). Keep in mind too that it can be an expression of anxiety. The copper rollers though too can promote salivation and thus a soft and responsive mouth.
Generally, the thicker the mouthpiece the less severe (though take into account the horse's mouth size and shape, that it can accomodate a thicker mouthpiece) and the shorter the shanks on a curb (the lower the ratio between the shank that extends above the actual mouthpiece, that attaches to the headstall, and the portion that extends below, where the reins attach), the less severe. A port below 2'' will (likely - depending upon mouth conformation of course) not interfere with the palate yet will offer tongue relief (especially with a horse who's collecting)...though it will exert a little extra bar pressure. A solid mouthpiece that is shaped to the horse's mouth (curved) can be relatively gentle as well, as can a double-jointed mouthpiece (though there's some extra tongue and bar pressure there as well). A single joint in the mouthpiece will exert a nutcracker effect on the tongue, though particularly if you are light on your hands, it is not usually a huge thing - just keep it in mind.
Corkscrews and twisted wires never have any place in any horse's mouth, IMO, so I have to say good choice in the change