A start, for educational reasons, and just on PinSide alone in the last 5 years.
If a person wants technical breakdown they are available on other electronic sites.

Some opinions are much better than others, do research.

Most restorers need two DMM for testing purposes.
A DMM is a requirement to keep machines fully operational, EM or SS, it does not matter.
Know the difference between a voltmeter and a digital multimeter.
Get a DMM and separately a logic probe, if not included with a full kit.
Make sure it has proper fuse protection.
Make sure it has 10 A range.
Preference to digital versus analog models.
Autoranging is a nice benefit.
Case insulation is available on higher end models.

An "old" DMM does not mean "bad", if it works well as this means "reliable", which better that most cheap junk today.

Cheap/Reliable - Radioshack True RMS 46-Position DMM $50

Serious/Professional - Fluke 117 and up DMM models series. Personal preference to 179 or higher, if you own many machines. Price range $130-$1000, including all accessories.
http://www.testequipmentdepot.com/fluke/dmm/handheld/index.htm

Ultimately, cheap tools mean cheap results, unless you are starting out.
A person needs to build a tool inventory, not buy it all at one time.
A person needs to buy their own meter out of preference.

https://pinside.com/pinball/forum/topic/best-value-priced-dmm-digital-multimeter

https://pinside.com/pinball/forum/topic/multimeter-choice

https://pinside.com/pinball/forum/topic/what-multimeter-do-you-guys-use

https://pinside.com/pinball/forum/topic/need-to-buy-a-meter-which-one-and-why

https://pinside.com/pinball/forum/topic/good-enough-multimeter

https://pinside.com/pinball/forum/topic/multimeter

RadioShack "Old Style" True RMS DMM (Digital)
1a016ae9e487f3c05fd8db1e038a7041.jpg

Fluke 179 DMM
http://www.testequipmentdepot.com/fluke/dmm/combo-kits/179-eda-ii.htm?ref=gbase&gclid=CjwKCAiAxuTQBRBmEiwAAkFF1jebhgoZ_XjSFhtrMVLRnY-LzLmPpPDrXcrJlxCSWRse_uNWdO0v9hoCj7MQAvD_BwE
F-179_Maglite_kit_01d_c02.jpg