I've not played with the wu-1a as yet, but the mc-dc2 does connect directly to the camera as you mention.
My own concern with the ML3 infra-red remote is whether it will fire reliably when outside in strong sunlight - I've had problems with IR being swamped by daylight before/reducing the range.
I'd not planned to buy the wu-1a as I genuinely think it should allow you to change camera settings from the app, which it does not currently do (bad design IMO), however I can fully appreciate it's use for remote triggering and also immediate review - I did a photoshoot with a family recently and it would have been excellent for them to be able to review the images in real time on the ipad (and saved me a lot of time after!).
I'll post an update when I have had a play with it