Arbitration ?

You should also know there is a difference between mediation and arbitration.  Mediation is non-binding...if you or she has second thoughts about what the mediator(s) have proposed, you don't have to agree or go through with it.  The downside is that you've wasted whatever money you spent on the mediator(s) and have to start back at pretty much square one.

Arbitration is a little different...the conditions of arbitration are binding.  If the arbitrator decides your stbx gets x, y, and z...your stbx will get x, y, z.  Bluntly, you may as well have the judge decide if you go the arbitration route as the result will probably be similar.  The only difference is that the judge will apply the law to decide what's fair while the arbitrator may not use the law and just decide what's fair based on their experience and whim.  Likely, your stbx's lawyer won't want her to go for arbitration anyways, especially if they have the law on their side, and you both would have to agree to binding arbitration.

I think that you're right.  Uncontested means that both parties agree on all the terms of the divorce.  If you don't agree with something, then you've got to agree before she files.  I'm not a lawyer, but that's what I understood from my states statutes on divorce that I've read.

How did your ex decide it is uncontested?  That is a decision for you to make.  If you don't like something she is trying for, you can certainly contest.  Sure as someone says, I'd certainly try the mediation route, but also as stated, have an attorney (one representing you) look over the final paperwork.

another option is starting off pro se (acting as your own attorney) meeting at her attorney's office for a mediation session and see where it goes - if you agree to to what she is looking for you can proceed and just hire an attorney for an hour or so to go over final documents with you to ensure it is everything you agree to - but basically handle it yourself.
If she was a stay at home mother or you make double or more than she does, she would be legally entitled to some alimony, even if it is short term.

it's not uncontested if she wants alimony and you want to eliminate costs. 

yes, you should talk to her about mediation. but she's already hired a lawyer right?  that may be tricky now. she will already have expenses to this lawyer.

but yes, you should.