OS updates without subscription?

Say I'd like to deploy dozens of small appliances, only use case is VPN.

Do I need to buy support for each of the endpoints?

My thinking is:

* When there is a problem I reproduce on a box with a subscription.

* It's way cheaper in the long run to buy a few more boxes than required and just replace them in case one fails.

For the rest I would be able to use a downloaded firmware everywhere I guess.

Why would I need a subscription for each of the boxes?