... I'm diggin' on that thumb lever operated type by IMA. I like that it offers bar-mounted .. and/or .. fork mounted options for the actuator and the fact that the kit is mostly complete, sans hydraulic line (that must be fitted to each application, so they're not included in the kit).
LINK = IMA Thumb Brake - Superbike Source Pty Ltd
Considering it includes both foot operated master cylinder and thumb operated master cylinder, and they are designed to work with one another, there's a little more confidence in it's trustworthy operation. The multiple ways the thumb lever can be adjusted is another well thought through feature.
$499.00 is actually reasonable, all things considered.
I think if the thumb brake is mated with a slipper clutch those two working as an ensemble will actually entirely change the way one rides. Everything from body positioning, right and left foot position on their pegs while cornering, and overtaking in corners will be rethought and adapted to the new ways of controlling the bike the slipper clutch used with the thumb rear brake as a combined ensemble will offer.
Every bit as revolutionary as foot operated gear shifting with left hand clutch was when it was adopted.
I really do believe this.
Imagine how useful it would be on motocross bikes! You could drive into right hand berms every bit as hard as left hand berms since rear braking is no longer dependent on the right foot being on the footpeg to operate the rear brake in right hand turns. Same with being airborne ... foot position on the pegs will no longer be dictated by the need to lock up the rear wheel in mid air to control the bike's attitude in flight. That can be done with the right thumb instead, so foot placement on the footpegs can be focused on body weight distribution rather than being able to operate the rear brake in mid air.
All of these wins! So many wins! I'd bet money left hand rear brake systems will become standard equipment sooner than later.