As I cannot find another Dashcam that has exactly that features especially small stealth cams+blackbox I decided to risk it and order a K1S via Spytech UK, as it costs me nearly 160CHF and can be returned if it does't work. Additionally I will get a Thinkwave F50 used only for parking surveillance.
Thank you all for the warnings regarding reliability which made me search:
after reading techomoan's review AND all the comments below and a lot others found on Amazon etc. I came to the conclusion that 90% of the problems with the k1S come down to 5 main issues:
1. SD Card: most failures come from a "wrong/incompatible SD card. Common solution was a lexar 32GB U3 Card works
2. Battery: Stock factory batterie sulfates and therefor overheats + damages the DVR Blackbox, can be replaced with GoPro 4 or earlier batteries
3. Audio: very low level of Audio recording.
4. Origin/manufacturer unknown: K1S from somewhere unknown, not official retailer etc and is it really a K1S or only looking like one with no support from seller
5. Cableing/Connectors: Connectors are very sensitive...
4 of the issues are non for me:
1. SD Card: I will use the Lexar 32GB u3 card that proofs to work
2. Battery: no issue at all as I will use the K1S only while driving/igintion on and install it without the battery. so no additional costs for a replacement battery too.
3. Audio: I don't need audio
4. Origin: I will get mine over Spytech UK/Amazon, official retailer and support available.
only number 5 can be an issue plus the rest 10%: no risk no fun....
5. Cableing/COnnectors: experience with cabling so I do my best to get the 4 USB Connectors stabilized, e.g. 2 drops of hot glue when connected and a tiny bit ice spray directly(!) on the drop and it is fixed to the box itself and a little push still releases it without any issue to connector...if my DVR unit has an issue there is warranty and send back to Spytech.
=> will test it for some weeks freely wired (except of the DVR 4 connectors, here I will be very careful) and lets see how it works. If not sent back and 20 bucks lost on postage, if it does I get what I was looking for.
...looks like I will have a bit more interaction with the DVR unit than original planed so I will check if I can stealthy mount it somewhere in the center console e.g. ashtray...instead of the glove box.
Additionally I found out that Innovv has waterproof cameras for motorbikes for the K1S which I can also use alternatively. So if K1S is ok perfoming I will install the cameras front in the front grill and back at the number plate so glare&windscreen problems are solved and even more stealth...