Earfun Free Pro 2 - sample variation (Patreon)

I wanted to bring up this issue again as I just checked the response of 2 other Free Pro 2 units I got recently and like visible from the measurements they differ quite a bit compared to my reference unit and also my other 2 units I am using regularly. I had another unit which I purchased recently for a friend and when I measured it, it was more inline with my previous units, therefore I don't know if this difference is just random or based on different production batches. 

You can see the raw response on top, the final response with applied tuning below, black being my reference unit  while purple and red being the other 2 units I purchased recently (I only measured those with pink noise, therefore there is some jagginess visible with bass). Especially the purple unit differs a lot, it’s not just a difference in amplitude but also the peaks are shifted, after applying the tuning there is more than 6dB treble difference, it would need a completely other setting to sound comparable let alone the same as my reference unit. The red unit although slightly better still sounds "completely" different to what I intended. The treble smoothness I get from my reference unit is gone here and it would also need additional tweaking to sound similar.

It would seem as if over time the production factory must have had some changes between different production runs, otherwise I cannot explain this strong variation and maybe this is simply what is to expect from such cheap prodcuts, but unfortunately it makes all my work become obsolete when looking at this variation. I cannot know how your unit behaves and if my setting applied will even make any sense. I am going to order a next unit just to get sure if these 2 units may be some spikes or if all recent units are simply different. 

Only solution for this would be to custom tune each single unit for those who really want the sound as close to what I had in mind. If there is interest, please let me know.