Ok, so my trial has finished last night. The whole experience was very positive, Three have done a heck of a job in my area (EN2) and I hope Enfield council will grant them further permission for many more installations.
As is usually the case there is a massive difference with Three between download and upload speeds, eg 300 vs 20-30 Mbps, but still that is very reasonable and more than you get with FTTC or Virgin.. and to be honest I can forgive them that because the prices are significantly lower than other operators.
Other than that the connection was extremely solid throughout the month with no disconnects, downgrades to 4G or packet losses. Latency was quite good throughout, around 15-20ms.
All in all, for now, I'd rank them higher than EE in my area for 5G.
Three have a great opportunity here to become THE "wireless" ISP of choice because it's just so much more convenient to plug and play a 5G router rather than wait for wires to be installed and so on, not to mention with multiple masts in an area you eliminate a lot of single point of failures.
So, am i signing up to a contract? Very tempted, altough I still have well more than 1y left on my EE one. The £10 I'd pay monthly for their unlimited data SIM (after cahback etc) would be affordable, but I'd also need to factor in the price of a 2nd 5G router. Decisions, decisions..