Looks simple and clean but I already use "remember the milk" to do the same thing. The landing page doesn't give enough convincing arguments to pull me away.
Exactly what I was going to say.
RTM has been around for a while and integrates with a lot more devices, they are committed to maintaining their Apps and provide much more functionality for power users with saved searches etc.
I'm a happy RTM user as well. This doesn't look like it does anything better, although I guess for people who don't need the more advanced features of RTM it's a good alternative.
Remember the Milk also has better device support.
I'm pretty unclear on the value prop.