Finally got around to ordering some 510 attys to try with my Bartleby. It didn't take long to realize I needed to PTB the cart for it to work properly, but now I see why the 510 is so popular. The vapor and throat hit difference between the 901 and 510 is surprising. It's a little harsh for some juices, but it will definitely "wake up" any juice that doesn't perform well in the 901. The PTB packs tighter too, which seems to work better overall.