About the best possible route is to upgrade the oldest device to it’s last available firmware and then update all other remaining devices to the latest firmware that still supports connecting to the oldest device via speedfusion. It’s not ideal from a security standpoint as there are vulnerabilities patches you may be missing out on. By having as many of the devices as possible on the newer version, you are at least lowering potential security problems.
From a features and stability standpoint, a lot of things will be patched or improved on the newer firmware.
The annoying thing about this approach is having to dig through the release notes on a bunch of firmware versions to figure out what speedfusion support is depreciated at what version.
I think that you can run
8.5.1 on the 580 and the 380 HW 6
6.3.4 on the 380 HW3 and still have these 3 connect fine
That would at least get 2 of them to firmware from November of 2024, it leaves the HW3 on firmware from 2017 though.
As for the 380 HW1 … frankly I am impressed it still runs, I think the latest firmware was 6.3.3. That was released in 2016.
I don’t know your use case or how important security even is for your situation but you should give some serious thought to replacing the 2 oldest devices. The 580 HW3 and 380 HW6 can both run current firmware.
If you want the cheapest out of pocket to do that, the B One is $300/each. Certain Speedfusion settings are paywalled behind a subscription but even without you can do 2 connections. They can do 3 physical WAN (by connecting one with a usb dongle) and 3 VWAN (at $200 each to activate) so they probably have enough connections for you. I have bench tested a 305 HW2 against a B One and the B One wins, it’s basically the same as your 380 HW6.
Talk to your sales rep at your preferred retailer before buying in case you have additional needs or would be better off replacing one of the newer units and transfering them to branch locations.
Your cheapest option is to do nothing and hope for the best. Replace them as they die and work out firmware then when you already have to put in the tech support effort to ensure it is all working with the replacements. If you start messing with it when it is working right now you could run in to issues that will tale troubleshooting time. I’m not recommending this but it’s been what you have done for quite some time.
If you do start updating firmware, start with the oldest model, log in and see what firmware it says it can download, update it, then do the newer models manually to the latest firmware version that can connect to the oldest. I can’t guarantee this but I think all of them have 2 firmware slots so it should be easy to roll back to the last firmware you were actively running if you run in to a problem.