Note most (all?) video players introduce quite some playback latency by default due to buffering - which is _really_ annoying using them as a 'monitor'.
I'm not convinced the mere fact that AliExpress sellers are not Sensirion distributors is sufficient to assume these sensors are counterfeit. Obviously there's precedence - buy a 'stm32' and you'll likely receive a counterfeit chip, but that's because these chips have been cloned by many. The Sensirion SCD40 is fairly niche and has an odd form factor - doesn't seem trivial to produce a convincing clone.
AliExpress sellers sell these at €14,99/1 whereas DigiKey is at €16,38/600 (excl. VAT). Price seems 'right' to me.
I have been looking for a comparison between sensors sourced from AliExpress and a reputable distributor, but sadly couldn't find any.
Anyway, I did get a few of these sensors off AliExpress for my personal projects. They definitely measure CO₂ (not eCO₂) - the only issues I've been having with them is the default calibration being off and a struggle to get the temperature reporting right (the sensor suffers from self-heating).
I ordered one SCD40 and two SCD41 sensor modules from AliExpress and I received them today.
According to https://sensirion.com/media/documents/48C4B7FB/64C134E7/Sens... (page 24) "All SCD4x sensors include a laser marking on the sidewall of the sensor cap. The laser marking contains the product variant (i.e., SCD40 or SCD41) and the product serial number within a data matrix".
The SCD40 sensor that I received has the laser marking on the sidewall of the sensor cap, but none of the two SCD41 sensors has it.
The price was ~€14 for SCD40 and ~€16 for SDC41. On Digikey they are currently €16.26 for one SCD40 (in a batch of 600) and €21.10 for one SCD41 (also in a batch of 600).
What do you think is the lilelihood the SDC41s I received are fake?
You'll want to look up the flags/settings for low latency playback to make it more usable, e.g. for mpv: https://mpv.io/manual/stable/#low-latency-playback