Just received my Hammer + additional stems. Like everyone else mentioned, it is smaller than I expected (...that's what she said?).
Let's get the bad stuff out of the way first:
The stems are made from really thin glass - I'm not sure I've even seen anything made from glass that thin before (I guess lightbulbs...). The glass is roughly half as thin as the solo stems. I don't know why they are using glass this thin, considering there have already been an above average number of reports on broken stems, and these are supposedly a revision as well. I'm glad I bought an extra set on sale for $10, because I'm not sure $10 for one of these is a good price; it's almost like they're designed to break. If they're this thin then they should be cheaper; if they aren't cheap then the glass should be thicker, especially for a portable vape.
The stock stems seem to fit on the inside edge of the 14mm female gong connection I have (MFLB low profile adapter), but I added a bit of silicone tubing around the tip so it seals better and protects the glass on the stem. I was actually pretty nervous putting the silicone on the stem, worrying that it might shatter on me...
Draw restriction is there, but less than the solo, so probably isn't an issue for most people.
Despite writing a lot of words on the bad stuff, my first impressions are really positive. I don't mind the sound, it heats fast, no cords no batteries, and reminds me a lot of the ergonomics and feel of smoking a joint in a good way. I get pretty great hits even with minimal amounts of material.