This is a great Android phone, chosen by wirecutter.com as the best of the low-cost Android phones. But, it very difficult to get reliable information about which credit card readers work with it. The PayPal and Square websites don't list this model specifically.
However, I've tested the phone with four readers, and they all work:
PayPal:
PPH V2 Mobile Card Reader (earphone)
PayPal Chip and Swipe (Bluetooth)
Square:
Magstripe Readder (earphone)
Chip Card Reader (earphone)
(Square Contactless and Chip Reader not tested)
For all of these readers, you might have to restart the app or unplug/replug the reader to get things rolling. I didn't attribute that to Moto G5 Plus difficulties, since the same was true on my iPhone 5S.
Of these readers, I like the PayPal Chip and Swipe reader the best, and PayPal is better than Square (customer service is available, and fee is slightly less). Square also has a Bluetooth-connected reader, but it's more expensive than PayPal's.
If all you want to do is swipe, not read a chip, both Square and PayPal provide free readers.
Replies
You are going to need a Chip reader since all credit cards are moving towards chips and away from magnetic stripes. Since you have tested the phone with the readers you mentioned above it would seem that it is a matter of personal choice.
I have used the square bluetooth reader for several years and it has worked flawlessly for me. I use it with my ipad 4 and also my iphone 6s.
I also have the paypal bluetooth rerader that I purchased as a backup. I have had nothing but difficulty getting it to connect and it has constantly lost its connection within minutes when I was able to get it paired with either the phone or tablet. Many use paypal successfully but that not been the case for me as I was not able to complete a single transaction.. When it comes down to it having it work for me is all that matters. I ended up getting a second square bluetooth reader as a backup.
I wasted an outrageous amount of time with paypal customer/technical support and never did get it resolved and they did not send me a replacement even though they said they would because they determined it was defective.
The original PP Chip reader that looks like a calculator sorta is super touchy. The new style one that reads and swipes is great. I just used it last week for the first time. Paypal does update the Reader’s apps, along with you phone/tablet so make sure you have those updated before taking to a show if connectivity is at a premium.