Looks like firmware version 15.X is back in BETA
I noticed the email showed different new features. I wonder if one or the other is wrong?
Both DES and 3DES will not work on the 15.x version. I tried it previously and did not work. Meraki support documentation did not mention 3DES only DES but a call into their support and I was told both DES and 3DES not supported.
I've been running an MX64 as an internet firewall and an HA pair of MX84s as a hub of an SD-WAN all day with this firmware and so far, so good. Upgrading another set of sites tomorrow.