Kenko DGX 2x Teleplus Pro 300 with 60D

Hi Guys: I always get good advice from this forum, so here is another request. I have a Caon 60D and would like to get an extender. I realize there will be some issues associated with an extender, but would still like to extend the range on my 100-400L USM lens. The reviews I have read basically suggest I stay away from Canon. There appears to be some good words for Kenko DGX. I would consider either the 1.4x or the 2.0x.

Any advice/suggestions would be greatly appreciated.

Thanks,

Harold