How reliable is the "smart" brake detection on a $20 tail light? Here are some &quot;smart&quot; tail lights I found on Amazon:





Having the same looks, prices, description grammar, no-name random &quot;brand&quot; names and sometimes even stock photos and videos, these seem like each-other's knock-offs coming from the same factory.
While I absolutely love the brake detection idea, should trust these with the technology and execution?
Or is there a bigger brand that introduced this idea that I should go for instead?
The brake detection is based on an accelerometer, and is not a complicated feature.  I have had a similar feature on a Chinese front light and it worked ok from what I can see. So that's probably not a key reason to buy a branded light instead.

Amazon are often parasitical in these products - AliExpress charges $11 for a similar (same?) thing
https://www.aliexpress.com/item/4000239342283.html
Cheap lights, especially tail lights can post a risk of death, in that I have purchased cheap lights from Amazon (albeit originally from China, similar to this), and they went out with no warning (battery dead) on a high-speed road.  (Though apparently some or all of the lights you link to have a battery indicator feature)
The biggest problem with these lights tends to be:

small battery
excessive brightness draining said battery
lack of proper voltage-sensing battery indicator (about to die in 10 seconds is not good enough)

As a second light it would be ok, but I would not rely on it alone.
If you want a better product then a brand might well be better in several ways.
For example:

https://www.cateye.com/intl/products/safety_lights/TL-NW100K/
https://www.cateye.com/intl/products/safety_lights/TL-LD710K/
https://ride.lezyne.com/collections/alert-led-lights
https://buy.garmin.com/en-US/US/p/698001 - This is Garmin's actual radar light which gives you alerts for oncoming vehicles

The best quality light like you mention (and possibly the first) is made by Lupine:
https://www.lupine.de/products/tail-lights
The Rotlicht Max is 1680 mAh battery, the Rotlicht is 830 maAh
The AliX light is 420 mAh, the Cateye Sync is 500mAh and the cheaper model will be even less, and the Strip Drive Pro is 800 mAh.
Exposure are a similar quality brand to Lupine, and they have a 1500 mAh light
https://exposurelights.com/products/bike/rear-lights/blaze-mk3-reakt-peloton
and a 700 mAh light
https://exposurelights.com/products/bike/rear-lights/tracer-mk2-reakt-peloton
The Exposure &amp; Lupine products are clearly much better than the AliX one, but they cost 10x as much, so they should be.
By paying for a brand you might get better build quality, better attachment mechanism, weather sealing , packaging, marketing, larger battery, better documentation, support videos, warranty and so on.
I don't think you could go too far wrong by buying one direct from China and then if it turns out to be inadequate then upgrading to a quality brand later. Or you could just go straight to quality now.