I had ordered five M201 stainless steel attys a couple of months ago. After just breaking out my fourth atty a few days ago, I noticed this one was different from the last three I'd gone through. First difference is the exterior. This fourth atty is shinier and smoother, whereas the previous three were more matte.
With the shiny one, the threads are indeed more recessed and it only takes a turn and a half to attach to the battery. The matte ones' threads start much closer to the end of the atty and take about 3 turns to attach to the battery. Although the lifespan of the matte ones were a bit sporadic (one lasting a week, another a week and a half and the third, over a month), I liked the vapor production and flavor of these over the shiny one I'm using now, which floods easily and is still turning my liquid dark brown (btw, my diy liquid isn't particularly thick). This is a pain because now I have to constantly blow out the atty and rinse out the carts, rather than just topping off. It's only been a few days so I can't assess the lifespan of the shiny atty, but I wonder if this formation of dark liquid is due to the breaking in period (although I never had this issue with the matte ones).
Here's a pic of the two styles. I tried to get the best shot of the exterior and the threads. The one on the left is the shiny version and the one on the right is the matte version. Oh, and you can't really tell from the pic, but about 3/8 inch from the battery-end, I can see and feel a definite bump all the way around the atty. Anyhoo, my question is which one is the old style atty and which is the new? I need to order more attys soon but I may just resign myself to the M401, which I'm very happy with, if the shiny ones are the newer, but inferior attys.