I bought a metric buttload of them from NEBG last year. They looked at me like I was crazy, but I'm pretty happy about it
I wish I could find the taller ones. I have one I got with a tree from Shannon Salyer but I've not seen them anywhere else since and it's my only one. Currently housing an early pine. They show up on Bonsai Q a lot and their depth seems more ideal for some uses than others I've seen here.