Welcome to the forum.
Screen dashcams always have the screen go out, some times you have options to choose how fast, and some even not at all if you choose, but normally in seconds it go black.
Record all the time ( they all do that )
Overwrite old footage when memory card full ( they all do that )
Record on impact / G - sensor ( they all have that though personally i do not use it as after all the camera record all the time, so why have bumps from potholes fill up the emergency recordings folder )
event record with button ( they all have that too )
Segment size, they all have that ( but i have never seen 30 seconds, but 1-2-3-5-10 minutes seem to be the normal, personally i use 3 minutes )
Stealthy ( for sure yes, and most also are so no fancy chrome parts on the front and no flashing LED's, "fancy" cameras do seem to be popular in Korea )
Dis-mountable ( all cameras have a mounting base the camera can slide off, 2 channel systems have the rear camera plugged into front camera so that is +1 thing to disconnect / connect, personally i leave camera on windscreen all year )
FOV / Field Of View ( most cameras are around the 1 30 - 140 degree, some claim much larger, some times lies some times diagonal, but 130 - 140 degree horizontal are pretty normal )
Night vision ( ATM the best 1080p sensors are IMX 291 - IMX 327 and for 1440p IMX 335 )
Speed watermark ( it cam mostly be turned off so it is not in the video, speed can always be valculated from the pure video as X meters traavled in X time, and more accurate than cheap GOS module, you just need to measure distance between 2 things you pass by, and then take time from video it take you to cover that distance, a little math and you have exact KMH sped )
GPS antenna are pretty much standard these days
Size ( most are pretty / very small, it is hard to find a large dashcam, but some shapes do appear larger, the preferred shapes of dashcams seem to be the wedge or barrel / tube shape, photos online can often be misleading look for L - W - D size, and size of LCD screen to get a better feel for actual size )
Cabin recording, there are 2 and 3 channel systems that have this feature, we call them uber / taxi cameras, but the normal for 2 channel systems are still a front and a rear camera )
Reliable. ( that is the most important part of a dashcam, but no matter the brand / price you should never install and forget a dashcam, look over the recordings every few months, look for first and last recording in drive sessions, these should be from places you know like home - work - shopping - activities - family - favorite gas station and so on, nothing should start or stop on some road any distance from a known place )
WIfi is also just about standard now ( it is nice for doing settings, maybe DL a file now and then, but it is terrible slow transfer speeds )
OBS:
If you are big on Dis-mountable, then you have to be mindful a little, some systems like the new 2/3 channel system viofo A139 have the rear and cabin cameras on a thin coaxial cable, this is nice for installing them, but the small mmcx plugs they use i dont think are good for clicking in / out all the time, so the more popular way of doing rear cameras with a USB plug will be much better for dismounting often.'
Some cameras have the GPS antenna in the mount, some have the GPS antenna on a wire, if that is the case you also have to unplug the GPS every time you remove camera from mount.
Mount do get worn with frequent dismounting, this can create a rattel, some cameras come with a eva foam pad to fill the gap between camera and mount so there is no rattle, also fairly easy to DIY some solution to this if it happen.
Stealth: this depend a lot of the options in your car, some have a big array of sensors on the top middle of windscreen, this mean you have to mount offset to a side of it, or in some cases people have mounted off its surface so the camera can film out the windscreen below it.
You should browse backwards thru this thread to see hoe others have installed dashcams in different cars.
https://dashcamtalk.com/forum/threads/where-did-you-mount-the-camera-post-your-pictures.502/page-64
Some times getting a little creative with install is needed.
Get proper size memory card 128 GB at least.
