Price performance is quite passable

The lamp, with its 283 grams (incl. Battery) quite easily. Therefore, it is also comfortable to wear. The rubber bands are easy to adjust and can thus be adapted to the light head / helmet size. For me, the lamp has also fitted on a riding helmet. The lamp has a zoom function. Zooming is done by simply inside or slide out of the attached lens. As moving is very easy, I suspect that it sometimes can happen unintentionally.
The battery compartment has as described by others no rubber gasket. But I think a little rain should it survive anyway. The holders / clamps who close the battery compartment a very thin joint (right flexible plastic hinge).
The LED head is pleasantly small and is therefore also comfortable to wear because the lamp thus is not top-heavy.
The batteries are connected in parallel in the battery compartment. This then has a further advantage. The lamp works even with a rechargeable battery.
The switch is on the rear battery compartment and has 3 levels.
Stage 1: Light.
Stage 2: darker
Level 3: Blinking

Upload:
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At the headlamp a small hollow plug socket. For this jack a 220V mains adapter is supplied with. I'm not sure whether the Ladelektronik in the power supply or in the headlamp is. Beautiful it would have been if a USB jack would have been on the headlamp, then you would not have the problem of lost special USB adapter cable.
But I think for me, the problem is more likely to keep within limits, because I'm just going home invite my spare battery with an external charger, and then replace the battery always box. So that is charged via these adapters obsolete.

Batteries:
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The battery performance is not as printed, they only have 1300mAh. But here I have thought that I have to buy my own batteries.
I have therefore in the batteries a little looking around and tried and have become able to find the following batteries:

These are "only" given as 2500mAh, but they also deliver these.

Luminosity measurements:
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To realisitsch compare the luminosity with other lamps I've been thinking it's probably easiest at 1m distance (distance between the LED) to measure the luminous flux and the light out area (diameter). I have to firstly used a calibrated light meter. But I have also measured with an Android app "Lux Meter" and am on comparable values ​​(The uncalibrated app shows about 10% -15% more). It can be seen 2 concentric circles illuminated. The inside is always the lighter in addition you can still see a darker outer ring.

Wide angle setting:
500 lux 1m-diameter

Full zoom setting:
5500 Lux, 20cm diameter

Compare with another lamp:
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I liken the lamp with another that I bought on Amazon.

The brightness is much better in the 10 more expensive lamp. However, the LED head piece is considerably smaller and lighter in deserted lamp. so it is therefore necessary to carry less top-heavy and pleasant. Because the lamp is less bright naturally keep the battery longer.

Conclusion:
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The lamp does not match the description. But it is relatively well and therefore I keep as an alternative lamp.