Meraki did a great service by splitting the firmware trains between classic and catalyst switches. The two firmware, MS16(traditional) and CS16(catalyst) are the same train but specific to the hardware platform. A great number of bugs revolved around mixing of these two code-trains. Most of the issues with the MS390 have been resolved around MS15 firmware and with CS16 it's only gotten better.
With the MS390 firmware stabilized, we're seeing alot of adoption of CS16 in the field, it's quickly becoming a GA candidate. If you haven't upgraded yet, i highly recommend so. The -M hardware should ship with CS16, so we won't have to worry about any factory-firmware issues that impacted the MS390.
The new c9300-M hardware is a whole new software stack based on the newer firmware, and have been getting very positive reviews from the field already on EFT.
This is the Meraki way, we learn, refine and improve perpetually. Wrangling the Catalyst into dashboard was a challenge, not without some pitfalls, but with the dedicated firmware and hard work from engineering... we're starting to reap the benefits.
Thanks to all that have stuck with us on the platform, and for those that are still waiting on the -M.... we look forward to proving our resolve.
_Nico