The SCD41 seems to require a lot more manual calibration while the S8 is very stable - maybe once every 3 months or so, I'll see it reporting ~380 ppm in fresh air (which is actually within spec).
The venerable MH-Z19 is probably my second favorite sensor, ahead of the SCD40-series.
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).
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?