Hi Inset irises!
My point of view, yes....install the 11.1 update. As with any OS security update, it's critical to keep any device current pertaining to security.
Yesterday (November 1, 2017) I downloaded and installed 11.1 on my iPhone 5s without any issues. I did connect my power lead, be prepared for the update to take a bit to complete. My advice, if you elect to download and install, do so when you're not expecting any activity! When the install completed the phone required an turn on.
iOS 11.1 Features: All the new and hidden features
This document describes the security content of iOS 11.1.
For a complex review of Apple security updates
Please describe what problems you are having with MMS? It's hard to offer any direction without more details.