I think the 20w iSticks were junk but other than that I love my internal battery mods.
I've been using 3 of my iStick 20W mods since I bought them 3-4 years ago. Just took another 1 out of the stash 2 months ago. Had several more stashed and just bought 5 more in the last 3 months. They're my hairdresser's favorite iSticks, too, and she's got a real bad case of the "dropsies". She goes through mods and tank glass like crazy, so I keep a "reserve" of them for her, too.
I also have several 30W, but I don't like them as much. The airflow slots are different on them than on the 20W, and I don't like having to draw harder to get the vapor I want. Stash also has some 10W, 40W, and 50W ones, too. Have several local friends who use the tiny 10W for stealth vaping.