They flow great but some have lava that sticks to the sides. The lava has a cool transparent look to it that I really like. As for popularity I dont know.
I was interested because I found one at a garage sale for one dollar .Another question? Where do people find all the lamps they have? I found some at garage sales in the box ,silver streak no 22,25 for a couple bucks Also some Mids 05,02,03,21, etc People around here are afraid they are a fire risk.
I have not found a single lamp at a garage sale. Check your flea markets. There are a lot of flea markets that you will just see when driving through town and a lot of them do not come up in a google search for flea market. I have found a LOT of good stuff at flea markets and they usually go for $10-$15. You can also try hippie/stoner/head stores they sometimes carry them.
Online you can check out craigslist. I usually find my best deals on craigslist but lamps dont come up very often. I got 2 midnight starships with blue liquid and yellow lava for $10 each!!!
And finally you can try ebay. Ebay lamps usually go for a lot of money so you will have to watch for low priced buy it no lamps or auctions that end at weird hours.