I did a little experiment using my DBV and a certain amount of bud each time I loaded it. I went through 3 loads, all of the same size, just between .1 and .2, and marked down each time I took a hit.
With that amount, I got an average of 19 hits, this was also going through my mini bong in my avatar. But that really wouldnt add to the amount of hits I can get, so...yea
Use the tool it came with to stir and pack back down the herb every 5 or so hits.
And by a hit, or one hit, I dont mean a tiny amount of vapor, Im talking enough vapor each hit to hold in for 10 seconds and still exhale a good sized cloud. I was really "blowin clouds(of vapor
)" haha
Everyone has a different standard. I defintely think its considered "efficient", just not AS EFFICIENT as some other units....