Easy and fun banner, good picture, make sure you check what events are on at the town hall before starting the banner as some events may affect your ability to reach some of the portals.
Drifting GPS/dodgy signal may make a few of the points tricky to reach so maybe try completing first thing in the morning when its less busy.
Did this in March 2019, Love the picture, took around 3 hours to complete just walking and hacking, you'll cover a pretty big distance around the city centre so be prepared. I would recommend doing this either on a week day morning (avoiding rush hour/peak lunch break times) or at a less busy time during the weekend because 4G signal (o2) issues slowed me down quite a bit towards the end of the banner.
Completed today (20/04/19). Nice picture, fairly easy walk, think it took around an hour and a half to complete (forgot to time it properly) Just walking, hacking and filling portals. All areas are accessible on foot.
Starts down by the docks and ends near Lime Street Station, tourists may want to get their tourist things at the docks done before starting the mission because you will move away from that area fairly quickly.