I was a player for the Starfinder Beginner Box adventure, but helped the gm set up most of the game beforehand, as I’m usually the gm for pf2e. First off, it seems both the bb itself and the starfinder bb-system available for foundry is an early version off the starfinder-system. There are some systems and concepts that are entirely lacking from the bb, like the stamina-system and the resolve points. The character sheets are also different, with some skills and abilities named differently from in the final version, by all appearances.
Another issue is that the foundry starfinder-system itself is a lot less developed than what we were used to for pf2e, with quite a few features and automations not present. This is mostly a QoL-thing, and most people not used to the foundry pf2e-system won’t notice it. Some of the most useful addons will of course work, like dice tray, drag ruler and token HUD (classic), but there are a lot less available for starfinder.
Otherwise, we had a good time playing starfinder in foundry, and having set up the bb in the normal starfinder-system (not the bb-variant) we saw no showstoppers going into a proper campaign. We’ll have to see if the opportunity arises :)
It’s really the only way to see how it works, so have at it :) Feel free to ask if there’s anything else I might answer for you.