One of the major worries with untreated Afib is that it will trigger blood clots that cause strokes. (Not to mention other possible side effects of not treating the condition)
Modern cardiac event monitors that the patient tapes onto their own chest, wears for a period of time, and then mails back in for analysis are so much cheaper than treating a stroke that it tilts the playing field.
Many people have mentioned a Holter monitor, but those are not only more expensive, but would be overkill as a first step in seeing if there is a real issue.
Here's a comparison between a Holter monitor and one brand of a more modern cardiac event monitor.
https://www.medgadget.com/2014/01/zio-wireless-patch-may-be-...