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I have the GS 35 Mini, it is supposed to be around 240 lumen, the one you linked to should be brighter even though they use the same lighthead.
The quality of those lights is quite outstanding, they are "Made In Germany"
One thing some people may get hung up on is that they only use one o-ring to seal.
Had mine to 100ft and it performed flawless, they are rated a lot deeper than that and the manufacturer is well respected in Germany and (over there) has excellent service.
I have also used and seen many different versions of their halogen "lantern" handheld lamps, that style is quite popular in Europe but not my cup of tea...
Compared to for example the Intova 4.7w lights it is brighter but it's also more expensive and you might not get any service for them here in the US...
Another thing about that particular series is that you can change lightheads from spot to flood and also different color temperatures and brightnesses, they have one available with presumably 700 lumen.
Hope that helped!
I'll go ahead and take it apart and post some pictures later today, just looked at it and it appears to be sealed but I'm not 100% certain...you can switch the LED out though, that may be accomplished through the lens element.
Edit:
I just looked at it again, and it is definitely NOT sealed. There are drilled holes in the aluminum between the front reflector compartment and where the LED mounts and contacts the battery.
My brother has a GS45, if I remember correctly the thickness should be about 3mm, they are very sturdy, I would not be concerned about denting one...I'll have it here by the weekend and can measure exactly if you want me to and post some pictures as well.