A few months back, I gasped in horror at the sight of a third-party Wii U pad that, from the hideous photoshop promotional image, looked to be a sin against everything Nintendo held dear about controllers.
Well, for the past week I've been using the thing. It's called the Controller Pro U. Combining the functionality of a Wii Remote with that of a Wii Classic Controller in the one device, there's not much hideous about it. In the flesh, it looks a lot better than it did in that mock-up.
It's Good! - Surprisingly, for a third-party controller that doesn't even ship with a brand name on it, this thing is pretty well made. It's got a great, rough finish that feels good in the hand (no doubt helped by the fact it copies the already-comfortable Wii U Pro/Xbox 360 design), the face buttons felt responsive and the thumbsticks were great, with a nice "tightness" to them that allowed for a lot of precision.
Versatile - The pad works on the Wii U, Wii and even Android systems (via Bluetooth). Note that while it works across systems when playing Wii games or Wii U titles that support regular motion controllers, I couldn't get it working (nor is it advertised as working as) a Wii U Pro Controller. What's really neat about its flipping switches is that it can trick the Wii U into thinking it's either a Wii classic controller or a Wii Remote. Meaning, yes, you can play New Super Mario Bros. Wii U with it (the official Pro controller won't work with the game).
D-Pad - I'm going to give a special shout-out to the d-pad, which manages to get a proper Nintendo design on the thing. I'm not sure how they got away with that, but it doesn't matter, it's a nice thing to have, especially on Virtual Console titles and Wii games designed for the Wii Remote's d-pad.
Shoulders - Disappointingly, the shoulder buttons weren't quite up to scratch, especially the triggers, which felt a little "floppy". The bumpers also felt a little loose, with pressure having to be applied right in the middle, or you might not register a press.
Were it not for the shoulder buttons, I'd recommend the Controller Pro U as a must-buy for Wii U owners, both for the quality of the rest of the pad and the sneaky versatility it offers for games that use Wii Remotes. With that slight disappointment, though, I'm just going to recommend it as a good third-party option, one that gets upgraded to "very good" if you're still playing Wii games or really want to play New Super Mario Bros. Wii U with a proper pad.
If it's not already available in your region (it's out here in Australia, for example), the Controller Pro U will be available soon from GameStop, Target, Walmart and Amazon. They'll be priced between $35-40. It'll come in five colour schemes: white, gold, North American SNES, PAL/Japanese SNES and black (you can see pics here). I'd say go for the SNES ones if you can; the gold looks a little garish, and I was also sent a black model, which with its glossy finish looks a little cheaper, and also attracts fingerprints just by looking at it.