Yup, the oft-repeated "does rank matter" thread. Not going to answer that one. What I am going to answer though, is that a teachers ability to be clear and concise and a good mentor might have nothing to do with rank. Some people are born teachers, while others have to work very hard at it, and others never get it, no matter how high ranked they are.
Watch a class and see how he conducts himself and how well his students are doing. Check out the general atmosphere of the dojo, and whether it is friendly and welcoming or whether it is militaristic (some folks like that style) and whether it fits with what you are looking for. I personally think one of the best ways to get a feel for a teacher is through their students. If their students are doing well, and are sincere in their practice, and they have a good attitude, then in part it comes from the teacher (of course, it also comes from the students). Don't get hung up on someone's rank as a teacher, as you might miss out on an excellent opportunity.
Lastly, my teacher once told me jokingly, that I was one of the slowest people to progress. After seeing my totally crest-fallen look he said "it is okay, the slowest learners are often the best teachers". While this might not be the case with me, I have seen this first hand. Often the stars in the dojo are not good teachers. Things come too easily for them, and they don't have the requisite empathy. Of course it is totally dependant on the individual, but, give this guy a break and go and check him out; and please do so with an open mind.