I've been buying these for 10 years and prior to finding these shirts I was literally wearing 8 layers under my top shirt to contain my sweat.
I have to be honest though, even new these shirts require to be doubled up for my level of sweat. They also take days to dry due to the highly absorbent arm pits pads. And they significantly deteriorate over the years.
I wash after every use and they last about 6 years before they become fairly ineffective. To ensure I cycle them effectively, I have created a numbering system to ensure I pair an older shirt with a newer shirt when doubling up. My oldest batch of 5 shirts were number 1, second batch 2, etc. I've just bought my 6th batch in 10 years - but well worth it. I have had to throw away the batch 1 and 2 shirts, and the 3's will be on the way out when the new batch arrives. I always have 15 shirts so that I have a complete week of 7 days to double up the shirts. Honestly it has been life changing and I would be a shell of the person I am today in social situations if I didn't have these shirts available.
I would love for the pinky skin-tone shirts to be more of a light beige to better match the light skin tone (I don't think anyone has the skin tone colour of these pinky shirts...). Plus adding a grey shirt would be great as this would go better when wearing short sleeve top shirts - as the bottom edge of the undershirts poke out white is very visible in the colours currently available.
Also, a really important thing is that the seams don't have the irritating plastic that appear in the cheaper shirts found out there.