MDM probably has other benefits I don't know about, but for these two examples you give, nothing special is needed.
For updating and automatically installing newly purchased apps on each device, just turn on "automatic download" and "automatic update" in "iTunes and App Stores."
For locating the devices, just make sure Find My iPad is turned on, then you can track the devices using Find My iPhone / iPad app or from the iCloud website. This is another reason to keep all iPads signed in to the same main iCloud account in iCloud itself.
You are correct, MDM doesn't offer anything special that you cannot accomplish using the more cumbersome and term and condition breaking methods you've listed.
Here's what you are missing:
1) Overview of each and every iPad, location, connectivity, ect from one screen when they are on separate accounts
2) Licensing apps to keep you from violating Apple iTunes agreements.
3) Cost, for your organization an MDM such as Meraki would work perfectly and is free.
You've state you have 12 iPads; App Store apps are only allowed to be shared with 10 associated, non commercial devices. Running them in a fire truck treads upon the boundaries of, 'Is this commercial or personal?' Nonetheless 12 is not allowed, you will need at a minimum two iTunes account to be in compliance. Of course all of this is at your risk assessment. Companies I've worked for also push the boundaries ( County Offices ) of commercial. They have all chosen to purchase multiple licenses instead of sharing a license. This also makes it easier for the accountants and potential legal action from the new lawyer trying to make a name for themselves.
You can absolutely go to iCloud and look up each device and find it's location. Try locating all twelve quickly and see how fun that is, especially when you get them in compliance with Apple Terms and Conditions. Try seeing which iPad is currently at the location of fire1 and fire2 and which are currently enroute via iCloud. I'm guessing the benefits of an MDM will be immediately evident.
MDMs also have additional benefits for your organization: sending modal alerts or banner messages to each device from a single portal. Remotely unlocking the passcode that your employees will eventually set and forget, never mind the number of times you ask them not to or tell the passcode to use. An MDM really shines when considering scalability and accountability.