Hi,
Here's some light reading regarding simulcast:
https://www.snewiki.com/wiki/index.php/Simulcast ...actually and viewing as well, as the YouTube video that's linked there offers a simple but thorough explanation of the effects of simulcast distortion.
If you are going to be a serious listener to the aforementioned new MSP system, when it arrives, the SDS models will be your best approach. Also as mentioned there are numerous conventional P25 departments that are using simulcast as well, and if you're smack in the middle of those tower sites you'll have problems with anything but the SDS in most cases.
New Bedford PD to my knowledge is NOT using simulcast. That system has been online for a long time. Departments that are switching from analog to P25 conventional operation as often as not seem to be using simulcast systems now.
Also, you have the Rhode Island statewide system reasonably near to you (aka RISCON). All of its sites use simulcast technology and this is another consideration.
DMR and NXDN are alternate digital radio protocols. In these parts they are primarily used by businesses, school buses, occasionally hospital security, and as Gary mentioned, some public works departments. If your primary monitoring targets are public safety there is pretty much no need for them for the most part. One good things with Uniden scanners is that these optional upgrades are priced the same regardless of when they are applied, and do not require the user to send them either to the point of purchase or Uniden for them to be done. Instead, a serial # and checksum # are obtained from within the scanner's menu, provided to the point of purchase, and in turn a key that unlocks the feature is generated that is unique to the scanner. It is then entered by hand which unlocks the feature. We have a multitude of information here regarding usage of both DMR and NXDN in the New England area, and the Radio Reference website, which is the source of the database used for Uniden's SD card based scanners (and third party software with a subscription to them) is another very good source of information.