I inquired to the company last year. Here is what I got:
Hello Mike,
Thanks for considering the Boomkicker! The U20 model K07U20 is shortened a couple of inches to better fit the area above the vang and it has specific installation instructions, but otherwise it's a standard model K0500. It should support the boom with mainsail flaked on top. Price from us is $217 with free ground shipping.
Assuming the mast track stops above the gooseneck, the Boomkicker mast bracket can be attached direct to the mast using the drill and tap included. The loads are relatively light compared to the vang. Some customers with carbon masts have epoxied a block to the mast then screwed the bracket to that to avoid drilling into the mast itself. If you have internal access you could drill through and use the included slide as a backing plate.
Let me know if I can help further. No matter where you get it feel free to contact me if you have any questions.
Thanks,
Ted Corlett