(Google) Plus Codes - or Open Location Codes - have many good features, and, to my mind, are perhaps the best of the systems to make lat and long co-ordinates user friendly - see https://github.com/google/open-location-code/wiki/Evaluation-of-Location-Encoding-Systems for some discussion, and https://en.wikipedia.org/wiki/Open_Location_Code for a description - they can be coded and decoded manually if required.
But they suffer from two problems: firstly, too often (yes, Google, I'm looking at you) they are given in short, local, form (e.g. XM9C+84, with a nearby city) rather than long, global, form (the equivalent of giving National Grid references without the 100km grid square letters) - yes, easy and good for local reference, but you often need the full version; and secondly, neither Google, nor anyone else has really pushed them.