We have several templates that we have many devices bound to and I am curious if anyone has run into any issues after updating a template. From what I understand as well it will update all of the bound devices to that template, has anyone had any issues with that as well.
It does as you expect. There will be a range of times for firmware to apply to each bound network, usually 5-10 minutes between each network. I've never had a problem with template firmware changes.
I have had the same concern with our networks, They are scattered over a bunch of different time zones and the concern is that you cannot individually update them during optimal times as mentioned in another comment they update about 5-10 minutes apart. Meraki HQ has the ability to update individual devices (secretly found out while troubleshooting with them ). Since finding that out, I hassled them and they mentioned that this feature is currently in the pipeline but unable to give any insight as to when it will be available.
There is a beta feature (which you can ask to be added to) for doing this but only with switches.
We have had no issues around this. Albeit it is worry that if something goes wrong you could up having a lot of angry customers!
The only thing to note is that when there is a new firmware released all Organisations Admins get an email about them being applied and there is not way to change this. So whilst automatic updates are a good idea from one prospective from another you need to make sure all Organisations Admins are aware they may get an email.