I am a bit surprise that there isn't a Juul tear down in this forum thus far... I found some juul tear downs on youtube mostly focused on looks and ease of use, but none done by EE people like the folks here who can comment on the electronics inside.
I can tear mine apart, but I am afraid I don't know enough to make good assessment of the electronics inside. Consider this an invitation for someone with a Juul and want to share your expert opinion on what's inside...