Sidemount Wimberley Head vs 4th Generation M-3.6

I have the Wimberley Head® - Version II which I love and I am looking to add a 3rd gimbal head.

Would like some feedback on the Sidemount Wimberley Head & 4th Generation M-3.6 from owners.

http://www.naturescapes.net/store/im...-gimbal-01.jpg

1 pounds 8 oz

http://www.naturescapes.net/store/im...h-200-s-01.jpg

2 pounds 5 oz

Planning to use this on a 3.9kg lens like the Canon EF 500mm f/4L IS USM with a Kirk replacement lens foot.