Since I got interested in vaping, I had always heard about "logs," but always thought it was extremely difficult to find good information. Fast forward a couple years and I am a VERY SATISFIED owner of an Underdog, my daily driver. Still curious if anyone knows more about these styles of vapes. Was the Purple Days the first? How long have they been around? Why have they always remained more of a cottage industry? What are the significant design features that have evolved through time? How are so many manufacturers able to carve out tiny little shares of a relatively small market? Just kind of curious to know more about this style of vaporizer. Thanks!