Is it useful (and polite) to ask a potential meditation teacher about their attainments? In another question, it was discussed whether it's possible to recognize if someone is an arahat. I'm interested in something slightly less formidable, namely the "attainments" that may lead to enlightenment.

Specifically, if I want to choose a Buddhist meditation teacher, with an expectation that I will, under their guidance, attain some or all of the jhana absorptions, and also the various stages of insight, is it appropriate to ask them how much of them they themselves have achieved?

One reason I think this could be useful is that I am very well aware that there is a difference between knowing about those attainments -- and maybe even knowing great detail about how they are achieved -- versus actually having achieved them. I, myself, have read around the topic a lot, and could pass for a teacher to someone who knows nothing. But other than possibly access concentration, I am an unattained noob. 

Is it worth asking others, so I can avoid a blind leading the blind situation? (Of course, there's the additional problem of knowing if someone who claims they have attained something is telling the truth. But at least by asking I could identify honest unattained noobs)

On the other hand, I recall a story of a very early teacher who in fact was highly effective and led many people to enlightenment without himself first being enlightened. (The story ends well in that finally he got there, but it may be a counter to the argument that to help someone to attainment X one must onesself have attainment X).
Worrying about whether something is polite or not is a hindrance. I am sure some practitioners would find it offensive but if they are offended that probably tells you all you need to know.
If you have yet to obtain the Jhanas then there are probably others who are still more advanced than you who have not yet obtained them either. The way I see it, anyone who is beyond you can be a good teacher and anyone who you are beyond can be a good student.
According to the Thana Sutta:

It's through living together that a person's virtue may be known, and then only after a long period...
It's through dealing with a person that his purity may be known, and then only after a long period...
It's through adversity that a person's endurance may be known, and then only after a long period...
It's through discussion that a person's discernment may be known, and then only after a long period...

You can't really know simply by asking.