Please note the £17 version comes without a UK plug for the charger and only one battery, which may explain the price. I got round this using a travel adapter plug.
Also the battery looks a bit 'cheap' (at least to my eyes). The top and bottom of the battery pack are capped with card inside the plastic casing so I have duct-taped the ends as a safeguard against water ingress (I'm hoping the card wasn't for 'breathing or cooling purposes) I used it in pouring rain yesterday and all stayed dry.
As I have only had it a couple of days I cannot report on battery longevity.
The light unit itself is very well made from aluminium with a glass 'lens' (it's flat and non-focusing so not really a lens).
It came without instructions but is easy to operate: press once for full power, twice for lower, again for lower still. Press and hold for flashing.
On the flashing setting it is far too strobe like so I won't be using that.
When connected the on/off button glows green all the time, this cannot be switched off, so I leave the battery disconnected when not required.
Other than that, yes, it is a hell of a LOT of light for £17.