Product review (4 stars): Actually fit. Wasn't awfully expensive. Measurement is misleading.
I had to replace the fan and insert in my over the range fan setup recently due mice falling into it and dying. I can get into why that was happening here but it isn't really relevant to the review. Lets just say whoever installed the original really half assed it and I'm still living with some of the consequences as a result. I decided to replace everything since the old one had some rust and obviously was gross.

Anyway, I had a really hard time finding any power packs or liners that seemed to fit the hole. I actually passed this one over several times because its listed as 30" and the hole I have is 28.5". I don't understand what nominal means in this context still as my total cabinet width is still less than 30" but regardless, this measures 28 and 7/16 inches wide. I found this out from the spec sheet on Broan website, which actually isn't super easy to find. The depth measurement is 17 1/4 inches from this same spec sheet. Additional information is available on this spec sheet which can be found by searching just for the part number.

The width was perfect for my cabinet but the depth was a tiny bit to short for mine. I solved this by buying a piece of metal plywood edge guard and attaching it to the wall to fill the resulting gap. It isn't perfect but it looks reasonably nice compared to a void or a piece of wood.

The metal looks quite nice and smooth and while its overpriced for what it is at least it isn't also poorly made. And compared to the few other possible options I had it is sadly very affordable. I used it with the cheaper power module of the two that fits. One thing to note is that these modules install flush to the face of this insert. The module I was replacing hung down entirely beneath this with none of the fan or light assembly actually inserting into the liner. I mention this because I had to modify my cabinet with a sawsall, hacksaw and lots of swearing because the power module hit into a useless cross piece of wood inside the cabinet hood facade and I had not anticipated it. Check the measurements on the power pack you use and use the spec sheet to determine whether you have clearance.