Do you mean the conventional (if you can call it that) Mikmar design with the jointed mouth piece? they do work, they warm up quickly in the mouth, there is enough in there to interest the horse, they can be a little bulky in a small mouth, but that is more of a perception of the rider than of the horse, because they are angled up the mouth they actually occupiy little space vertically and present a broad edge horizontally, so are no unkind. A word of warning though, you have to be scrupulous about cleaning them after use as there a lot of moving parts and they can quickly jam up if neglected.
If you mean the newer Mikmar products, I haven't tried them (most are gags of one sort or another) but I don't think they are as scarey as they look.
Thanks for both replies! Yes, it is the double jointed one with the copper roller I was looking at.
I need something that offers more control for jumping. My horse is a tad over enthusiastic and tends to bound in, ears pricked with too much speed. I use a Sprenger RS normally, and have recently tried a Sprenger Vienna which is better but I know it's rather harsh (I use 2 reins). I like the sound of the Mikmar offering more precision but that it won't hurt the Horse. He does like a contact in to the jumps. Really something that gives control but not too much of it!! I thought the one with loops would be good as it has the option of a wee bit leverage if I needed it. They do look interesting! I have to say $169.99 from Mikmar or £179.99 over here-I'd be ordering direct! The combination bit looks a bit too much, yes he's strong but not very strong!