Miguel,
The Lunasix-F does NOT accept accessories which have got electrical plugs, such as the flash attachments.
Indeed.
But it doesn't need the flash attachment, the "F" in it's name standing for "Flash", indicating that the thing is capable of metering flash as well. All by itself.
The Lunasix F is a Profisix that also does flash, and takes a bunch of the same attachments, but not all.
It takes the Tele, Lab, Repro, and fiber (the version without the plugs) attachments, but not the Color, Spot, Lux or fiber (with plugs). Nor the TTL-Select.
And the Profisix meters about (i forget the exact amount) 2 stops lower light.
All in all, i like the Lunasix F better than the Profisix, just because it does flash without large and expensive attachment. And it does it well too.
Get a Profisix if you need a Color or Spot attachment (the color attachment is fine, but the Spot thingy is i feel, far too large, Not that the Spotmaster is not...), or the small extra bit of low light level capability.
Else, get the Lunasix F.
Apart from the electrical fault mine all developed (mentioned them earlier), they are both very good, very nice meters.