Why is this ad "ideal for a budding startup"? I'm sure mixpanel is a nice place to work, but there doesn't seem to be anything unique about this ad, so I'm not sure why it's being held up as a model to emulate.
No false promises of using technology X or Y, and no over inflated expectations of the kind of knowledge expected from a candidate. A startup is all about learning and using the best tool for the right job with a hands on approach.
If a salary isn't provided my assumption is that it is negotiable.
I've found it's a lot easier to lure people away from their jobs with promise of 2x pay rather than trying to spin them on how awesome your company culture is.