I am using a 2013 Moto X Developer Edition (XT1053) and am currently running stock Android, (with the exception of Motorola's software) and I am thinking of switching to CyanogenMod. However, after looking at the CyanogenMod download releases for the "ghost" model, I notice there are pretty much only nightlys. I have never used a nightly release before, and I do have a nandroid backup if anything goes wrong, but are the nightlys stable enough to use daily?
You can't use nightlies daily, you can only use them at night. (<- That is a joke, by the way.)
Nightlies are the most unstable builds of CyanogenMod, but the number of bugs depends on the device. Typically, there are few bugs, as they still test the ROMs, but you will probably encounter (a few) more bugs than in a stable build. Most people will be able to use the nightly build as a daily ROM.
It is highly recommended that you make a backup just in case anything goes wrong, but you should not expect it to be filled with bugs. Remember, they test these ROMs before they upload them, so they are generally safe. Even so, you should refer to your device's CM changelog to see what they fixed and what to watch out for.
Back when I had a Samsung Galaxy Ace and wanted to use CyanogenMod on it, it almost always had a Nightly build. Encountered a few bugs, but not major ones.
Granted this is a different phone and CM version, point is you have to know which features/functionalities are working and not based on the wiki/release notes provided. Also which bugs are present. You may want to wait for those information to be available before flashing. But it's always good to have a Nandroid back up.
So, nightlys could be safe, could be not. Always refer to the documentation.
Look for the appropiate discussion about the ROM, for which xda is a good place. Usually, there is a reason why CM does not consider a ROM stable enough to tag the build as "milestone".
This does not mean it will be useless for you. Sometimes the ROM does not get the tag because something is not working like NFC or Bluetooth - and if you don't need that, you should be still fine.