The User Agent used by some sites (e.g. banks) to block old browsers is a little out-of-date and doesn't always reflect the system.
On my Mojave, Catalina, and Monterey systems, it announces itself as Intel Mac OS X 10_15_7 and Safari 16.2 even though I downloaded the version of Orion specific to each OS and the included WebKit is newer than the WebKit included with 16.2. This causes some sites to reject access claiming my browser is too old even though the included WebKit is actually newer than the WebKit included with versions of the browser they do accept.
FYI, the two most common sites I see used to check a browser version via User Agent are:
https://www.whatsmybrowser.org
https://www.whatismybrowser.com
I defer to others whether it makes sense for Orion to promote itself by default or match Safari's. However assuming the latter I recommend the User Agent string match the latest version of Safari that doesn't have a newer WebKit. For example, if a version of Orion is using WebKit 618.1.2 then perhaps match to Safari 17.3.1 as it appears Safari 17.4 is using 618.1.15. On the other hand if a version of Orion is using WebKit 619.1.1 then match to Safari 17.4 until a newer version of Safari comes out.
Then as far as announced OS version, I would match the actual OS version unless doing so creates risks around fingerprintering or OS-specific attacks. If not using the actual version is done deliberately to avoid fingerprinting, etc, I would at least pick a newer of the OS to project. For example, when pretending to be Safari 17.4 as above, project Monterey since that is the lowest version of the OS that can run Safari 17.4.
In the meantime, I just manually set my own Custom User Agent along these lines and made it the default so just suggesting this change to the default for other users.
Version 0.99.127-rc (WebKit 619.1.1)
Mojave (10.14)