The built-in flash is OK, like on most SLR's with a built-in flash, but it is no match for something like a Vivitar 283.
I have the user manual -- is case you didn't get one -- but I'm trying to find a PDF compressor that works on 250MB+ files so I can upload it.
In short, when using an accessory flash, the built-in flash will fire, and the aperture will be set to "about" f5.6 -- whatever that means. So set your accessory flash to assume f5.6. With a powerful flash, you can extend the usable flash distance for the camera quite a bit.
I hope you are left-handed. FYI, they also made a Z2-L which drops a couple of the fancy features.
Butkus' Z manual -- assuming that is what you downloaded -- is the English only version. Mine is in four languages, so it's a lot thicker, and a little more difficult to use. Otherwise it looks pretty much the same.
Anyway, happy left-handed shooting.
I find the Z (that's the only Samurai I have used) images to be super-sharp. It's up there with the Ricoh Caddy half-frame -- a great tiny camera (same lens as MOST Ricoh Auto-half cameras), but no zoom lens, TTL metering, auto-focusing, built-in flash, self-timer, intervalometer, etc. etc. etc. etc.