I'm sure the offer was legit.... Doesn't mean they won't be preproduction units..... Though with this chip, not as big of a deal, since it seems to be user upgradeable, so you won't be left out on any nifty changes between now and final product
Of course, that's speculation... But generally production units aren't run until beta is done, so it's a somewhat safe speculation

Sent with one hand, the other is busy vaping.
I think you were right in your first point - it's upgradeable. So as long as they have finalised the hardware side, which was probably done weeks if not months ago, they can make the physical units and then put the latest firmware on it before they ship out to any customers.
In other words, I would not expect any Opus 200 units to arrive in customer hands requiring a Day 1 FW update, unless they happen to discover a major bug in the time it takes for them to arrive in the customer hands (a few days) - hopefully unlikely.
There may well be an update in the first week or two though, as no matter how rigorous a beta program is there's always likely to be new issues found when a far greater number of people start using it. In fact I would take a week 1 - 2 update as a
good sign, of responsiveness; worse would be if one was needed and they took too long to provide it.
Fingers crossed Evolv have worked on the infrastructure necessary for this - a file hosting section where it's easy to download updates along with a changelog of their contents. And hopefully some system of communicating updates to the public at large, such as an email notification list.