Right then, Derah ... here's the verdict.
I went for a gentle plod of about an hour. It was clear night, with a half moon.
In semi-lit conditions (illumination from distant street lamps, nearby flats, ambient light in urban area) the "optimum" mode was fine. In pitch black, going into a copse and back out, I switched to "max mode" and could see clearly where I was going for about 10 paces ahead.
The light itself gives a kind of monochrome effect, a bit like very bright moonlight. But it's good enough to see where the path ends and the grass begins even if the grass is more grey than green. Even in the woods I was able to spot potential tripping and ankle-turning hazards like large conkers, litter etc.
I'd say it's great for routes you know well. I'm not sure I'd run at full tilt in pitch black conditions just yet with the headlight, nor would I go exploring unknown trails down by the river (!) But these are quibbles, really, for a piece of kit that cost 25 quid.
They claim a battery life of 120 hours on optimum and 100 on max output (presumably this is cumulative rather than non-stop). Even at half that, one hour a day five days a week will last months (it uses 3 AAAs).
It was comfortable on my head and I soon forgot I was wearing it. I did feel a bit of a pillock at first, though.
If you're more into rough trails you might want to look at a higher-spec model, but for my relatively modes needs in urban (ish) parkland and towpaths the Tikka Plus is ideal.
I wish I'd bought one of these years ago.
This has been a public service announcement in glorious Muttleymedia :-)