Depending on which cluster type you install, it can be a pain to get all the features to work. Some 2011 to 2012 Mustang
owners liked the 2013 and up clusters with the "information center" that provides the stop/start times, etc. Making that work in a pre-2013 Mustang can be a big challange. A nice write up by a member here and on another Mustang site helped out; I think that thread went to 20 plus pages of posts before they got all the bells and whistles to work. If you read through all the posts (recommended), you will see that several visits to a dealership for flashing was required (OP here already states that his dealership won't support the cluster swap).
Be prepared if you go this route.
About 8 years ago, I started a thread on swapping clusters in the 2004 to 2010 Ford F150's; many of the base models did not come with a tach (sacrilegious in a truck!), and wanted to swap out the cluster from a model that did have one. Depending on the model (STX, XL, XLT, Lariat, King Ranch, etc), their "information Center" would provide things like outside temp, door ajar, miles to empty, and that list goes on. Getting all that to work on a truck that did not have thiose initial features was next to impossible. I ended up using a cluster out of an XLT manual transmission cluster (all manual transmissions came with a tach) in my STX model, as it was the closest model to my truck that would have a tach.
Lesson learned from all that: it was simply not worth the headache to make it all work!