Underlayment for standing seam unvented attic

I am having a standing seam roof installed. I am also having an unvented attic with closed cell foam installed due to ventilation issues that can not be resolved due to roof design. My installer wants to install ice and moisture guard on the whole roof for rain protection because he is contracting out the tear off. He says it is not a problem with moisture retention in sheathing. My foam insulator also says it’s not a problem. What is your opinion on this underlayment? Is there maybe a better choice?

Its not a problem. Potentially overkill, but there should be no issue with installing Ice/water in this case.

I just had a metal roof installed the product is Exsteel storm seal small tab with exposed fastners with peel and stick ice shield over the entire roof and 1/2" plywood substrate, closed cell spray foam 5" and 1/12 slope. My question is with solid foam closures at the eve and the ridge cap made of bent pieces of storm seal instead of a vented ridge cap. I think I will have trouble with condensation forming between the tin and the underlayment, running down to the foam closure freezing and popping the screws off and eventually the wind blowing the roof off. What is your thoughts, should I be concerned?

Should be fine and what little bit there might be in the right set of atmospheric conditions should be minimal.