Ikenvape has had 2 sales now where their colored cartomizers are 1.50 for the 510 I believe. The KR808s were 1$ each. I can fit between 17-20 drops in the KR808 ones. I dont have a 510, so can't really help there.
I like the cartomizers, easy to fill, can grab a couple and be good all day when out and about. When I'm home though, I tend to vape a while, then pop the top off and drop another 5 drops or so in, recap and vape some more. Supposedly that'll keep them lasting longer. Cleaning them is easy too, boil wash and rice dry lol
I think the convenience of it is making them more attractive to some. I can't imagine trying to drip with lil ones underfoot or while driving.