Well keepsake, I had never vaped kief straight before, but I tried it because you asked about it. I have a mixture of kief from the trim of the 6 varieties of cannabis I'm smoking, plus grinder kief to compare.
I first tried the trim kief. I gently hand screened it myself and it is a beautiful blond. I loaded a quarter bowl in a stock dbv wand. I took one just massive hit that had me floored, and coughing for several minutes, but after that I took my normal quick 5-6 second hit and for the same lungful, for me, the kief seemed smoother. It caked up a bit at first then, crumbled a bit, but stayed sticky and chunky as it vaped. The flavor, while very intense and wonderful, lacked the freshness and complexity of it's bud counterparts. The perceived "freshness difference" could have been the result of differences in storage. The bud has been kept airtight. The kief is just in a ziplock, often left open. I know, I should put it in glass and keep it closed
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The grinder kief was a mix of Green Ribbon and Green Crack. It melted and bubbled so I only took a fairly small hit before I scraped it out, as I thought it may clog the screen. That stuff tasted amazing, much better than the trim kief, and although it may be because of the small hit, I felt it also was smoother than the bud.
This was pretty cool to try out, and I got really stoned, but for me, I think I will stay with just mixing the kief with bud. For me, a 70/30 mixture of bud/trim kief is perfect for an evening vape, as I find the trim kief to have a more sleepy effect than the bud.
I think that my comparison may be somewhat flawed as the temperatures for optimum vaporization of a particular kief is different (seemed higher to me) than it's corresponding bud, and I didn't pursue dialing in the sweet spot for kief and I wasn't comparing bowls of the same mass. It was an imperfect comparison, but I did get the feeling that for these particular buds, and the corresponding kief, that the kief was smoother. A different cannabis and kief combo could be different for all I know. I have only tested what I have, but I may try it again as I have a new 14mm set-up, and my above comparison was on the stock 18mm.
Peace and happy vaping to all.