If you have a CC Pro this is the one.
I wasn't sure what the difference could be between the Classic Linker and Classic Linker + until I got a CC Pro. The + works with CC Pro and the regular Classic Linker does not, so there you are!

Works fine with the Classic Controller on Wii
As another user noted you cannot change the button layout so you simply need to learn the new one. It works well with the Classic Controller and the PS1 dual analogue pad I tried using Gamecube games like Mr. Driller Drill Land or Midway Arcade Treasures (this was via GeckoOS, though I expect it would be fine on a North American system as well). With Metal Slug Anthology (Wii) you get the best game performance possible using either PS or CC pads rather than the Gamecube pad and certainly better than any Wii-specific control layout.

Given the cord length is so short a Gamecube controller extension cord is a must. It should also be noted that you cannot use both a CC and a PS pad simultaneously and you cannot swap controllers without unplugging the controller from the Wii/Gamecube and then reconnecting it or resetting the console.

Good
It works perfectly on Gamecube so far. PS2 Controllers and Classic Controllers both. The only issue I have with it is that you can't change the button layout at all. Aside from that it's a good product. It feels a bit flimsy, especially the cord doesn't seem to be attached that well, but I don't think this will create any problems.
EMS advertises that you can use a Classic Controller on the PC as well, via one of their GC to USB adapters. I've tested it with a 3in1 MagicBox and it works fine. I suspect other GC to USB adapters would work too. It just creates a bit of a mess with all the cords.
I have not tested this with the redesigned classic controllers, but it should work just fine, since functionally they are the same as the old ones.

Work only on ps2 pads
this don't work fine with classic controllers