Restoring from USB

You can do this but if there are drivers in Computer B that Computer A does not have in the ISO then you might run in to problems.  But if the HW is identical then you should be good to use the same ISO.  The only way to know for sure is test it by booting Computer B with the ISO file.

So the ISO does have device-specific things that install with it?

When you create the ISO from the Agent it can install drivers, etc. on to it yes.  It depends which options you select when creating.  But most of the time the standard ISO should work on multiple machines.  Again easiest way to test is boot Computer B with it and see how it behaves.

As Chris noted, there is a generic ISO that can be generated for recovery, but if there’s anything special about machine A that is different that machine B, it’s going to be best to generate the ISO from each machine to account for those differences.  If they are exactly the same, then you’re probably be safe to generate one recovery drive for both, but I sure as heck would be testing that recovery disk on both machines to validate that it works.

Just a small hint if you consider using a generic ISO (as @dloseke mentioned):

Please remember that in case you are using encryption you need to keep the key available. :-)

I can confirm the usage of a generic ISO but you might have to deal with driver issues. That could be solved in one of the later steps when restoring.