Yes, I wholeheartedly recommend the Retrozone SNES adapter to GC over the Hori Digital Pad. I bought one when they were first introduced in Japan (I think I paid like $60 for it!). It does a great job emulating the look of the SNES controller, but for reasons I cannot comprehend, the controller maintains the same Gamecube oddball layout of the face buttons.
With the adapter, you can play Gamecube and Gameboy games as well as Wii VC and a number of Wii games all with your classic real SNES controller all without any lag or cable splicing.
As for the Hori N64 Mini Pad, I also own one. They're expensive, and I'm not sure it's quite worth the price.
Pros:
-An excellent Control stick. It's similar to the Gamecube's but a bit looser and also slightly bigger.
-You can access all the buttons without having to change how you hold the controller.
-Supports all existing controller addons.
-Great conversation piece amongst videogame friends.
-Two Z buttons below L and R. Use whichever one you want.
Cons:
Just like the OEM Gamecube controller, the dpad on the Hori N64 Ministick is placed as an afterthought. Any game that is played with a dpad your much better off to just use a real controller.
-The buttons are too close together.
-Expensive.
If you still want one, check ebay.