As a new Flex user maintaining part of an existing project, I would say to be very cautious.
I haven't used robotlegs, but attempting to learn flex and robotlegs and convert part of an existing project to use it is a recipe for disaster.
In my experience companies are interested in quick results when in maintenance mode on existing projects and won't be interested in excuses when the new developer messes up an existing project by trying to introduce a framework they know nothing about.
Get comfortable with basic Flex. If you want to try RobotLegs, create a test project to play with.
Don't add robotlegs to a live project when you are not sure of either flex or the framework. Or if you do, start looking for your next job!