I'm not sure how you bricked "a few" of them, to be honest.
Normally, the switch will always "remember" the old firmware in case of corruption/failure of the new firmware. If the image is corrups or fails to boot, it should revert to the previous version.
The best way(imo) is to just stay on the stable release and only take action when the dashboard reminds you to do so. Ofcourse this assumes you have no need or requirements that are only covered in beta features.
I've upgraded hundreds of switches and access points over the years and I have never ever had one die on me because of this. Even in networks with 100+ switches in a STP-topology, they seem to just upgrade fine and in a sane order.
I'm not sure if Meraki itself can confirm this, but I also believe switches in the same network will agree that a reboot can be simultaniously triggered on all devices, minimizing downtime.(? can someone confirm this)