The answer to all my gardening problems? Perhaps not. But as Churchill said after El Alamein "it is, perhaps, the end of the beginning".
The sprayer holds up to 16 litres, but of course, the more you put in the heavier it gets, and I don't yet trust the slightly flimsy catch on the second shoulder strap. Instructions are very simple and rudimentary, only covering how to fill it. The wand head attachments remain a guessing game!
In use, it is comfortable to wear with about 12L on board: beware over-pressurising, or it will overflow and run down your back. This is a job for proper overalls!
But with it, I am able to cover larger areas than before, and this device makes light work of the job. I no longer dread weedkilling!