the Aldi ones I bought 4 years ago said bamboo on the packaging/marketing stuff, but actually had a significant % of cotton when the label was examined! Might account for slow drying? Fine for work or day walks when not working hard.
Bamboo is just the cellulose source - basically they are viscose - nothing new there.
After avoiding merino for years because of the itch factor (for me), I tried a Rab MeCo this autumn. works well and comfortable. Still smells after a day, but not as bad as most synthetics.