My own experience of EDI through the years was mostly sub-standard, so I doubt Covid-related issues have made much difference. On a few occasions in a busy security hall I have seen the change happen where bags suddenly flow easily through the scanner with no diversion to the "bag check" line which has backed up. It's understandable I suppose. Many passengers have two or even three trays - and get shouted at to take them all to the single tray area to refill their bags. Even LHR does this better.
Unable to board because the corridor is closed to allow arrivals from another gate ambling past was common enough - no big deal except for the subsequent missed TO slot / late LHR arrival / missed connection etc.
Arriving at EDI early, waiting for a gate/jetty/steps - not unusual. Deplaning onto a bus to be driven all the way back across the airport, stopping (it seems) every few yards for various traffic, to arrive at the newest/latest entry point - which then requires an amazingly long walk back to the arrivals hall. Hopefully you have no luggage to wait for - that can be a legendary period in which time seems to stand still.
Not all is bad - immigration has improved considerably. After the absolute shambles of the first and second versions of passport reading machines, they now work well and quickly.
To be fair, EDI is primarily a shopping mall with some nice eateries, and the world's most expensive car park. Sometimes they remember there is a runway attached....
Unless EDI is essential, personally I would take the train to MAN which is a better experience by some distance. NCL is good, but of course much smaller.