I have a Myler I use on Vida when she gives me grief. http://www.toklat.com/dyn_prod.php?p=89-L52435
I'm using it on her now since she had the winter off. I love this bit I think its gone up in price since I bought mine. I paid around $120.
She respects it and does what I ask when she's in it. I tried going to a snaffle, I used a JP Korsteel oval mouth snaffle for the first few rides but she had no respect for it so I went to the curb. I will switch back to my Imus comfort bit when we get a few more miles on.
I know I'll get grief for using a shanked bit, but we're both more comfortable with it and I know how to use my hands.
Heres mine, I'm pretty sure its the same one
They both look like they are made well and shouldnt harm the horse. The twisted one doesnt look that severe, the copper roller will help keep the horse soft and submissive, but does he really need it?? I think the best bet would be the full cheek unless you find he needs something a bit stronger.