It’s worth noting that the Convexa range is still currently based on 15.05 as well.
Convexa supports mesh as well. Mesh can be created without an app using the physical buttons which is both a blessing and a curse (it’s a bit of a convaluted process).
Other “advantages” of the Convexa series is:
3 Ethernet ports
USB port (which I really miss with the Velica as I used a memory stick as a video NAS)
You can SSH to each slave on the Convexa mesh which you can’t on the Velica mesh - I used to run transmission on one of my slave nodes)
The Velica does have better WiFi coverage in my experience however.
YMMV 