I KNEW I’d buy one of these WK20S’s some day soon. 
Just bought on Amazon US… using the code happily provided by Mr. Shao- THANK YOU SIR!
I HAVE the Sofirn SD-2 (and love it) so this should be a close “cousin” with more output. My wife and I WILL dive this light (and the new SD-5 I got last month) around X-mas time IF I can get to Cozumel with Covid and all.
Got the Wurkkos WK20S in today and went out tonight to check it out. But first I grabbed my Sofirn SD-02 dive light I’ve owned a few years now and compared them side by side- they are IDENTICAL host bodies. Basically this Wurkkos WK20S is an updated version of the Sofirn SD-02 with a different emitter and (probably) driver.
I took my IF25a out to check against the WK20S and the IF25A kept up in throw ONLY running at full speed— where it got hot very fast. The Wurkkos took twice as long to get to the same hot state as the IF25A (as expected). The beam on the WK20S was tighter than the IF25A, and the tint was a bit cooler (both my IF25A 6.5k lights are truly closer to 6k) and I could tell tonight with the WK20S being more blue and probably right at 6.5k as stated.
Before taking it out, I charged the Wurkkos battery in the supplied charger where I showed green (full) at 4.13V. So not a full 4.2V charge, but fine as battery life is better with the lesser charge anyway. I am sure I could get several dives out of one battery with this charge so all good there. I am guessing the Wurkkos (white wrapped) battery is the same 3kmAh as Sofirn’s (black wrapped) labeled 3k battery from what I could see.
The Wurkkos came in a nice color printed box with all the usual stuff: USB cable, single slot charger, a few spare o-rings, and a serious lanyard that is an update from the SD-XX lanyards I’ve gotten in the past. As a diver, I’d still add an extension from the lanyard to the light, but this is the first time a dive light came to me with a lanyard that WILL work in a pinch- with a nice rubber boot over the hand-hold side of the lanyard’s rope which is thicker and longer than any I’ve received in the past.
So a great light for diving here and I am hoping to get it underwater this December and report back then.
Who knows where I can get a replacement switch for the WK20S?
The actual internal switch, or just the button?
Former, no idea.
Latter, it’s just held in with the retaining ring and can be cleaned/scrubbed out thoroughly and replaced. Spring, too.