Hi @torntrousers, thank you for your interest in Cayenne, and welcome to our community forum.
MQTT device data history charts/downloads should be working OK now. Please note that you'll need at least 60 minutes of data (even if it is just one data point) before the 'hour' view on the chart will populate.
As far as the mobile apps, neither yet have MQTT device support, but we are getting very close. The iOS app update to introduce this may even come this week, depending on how our ongoing QA test goes.