I am having trouble figuring trying to sort out all of the many models of Gossen meters. Apparently, there have been many variations of the 'Luna Pro' series over the years. The same product seems to have different names in different countries, and different products have similar names. So far, I am not finding a specific model called the "Gossen Luna Six Pro SBC" - do you have a link to a photo or website which describes that model? Is that model different from the Gossen Luna Pro SBC?
The problem with the naming of Gossen meters arises because the US importer/distributor insisted on using a different name than the rest of the world used.
The meter that Sirius refers to is properly known as:
1) Gossen Luna Pro SBC in the USA; and
2) Gossen Profisix in the rest of the world.
There are a couple of other Gossen meters you might also consider, because they share the same 9 volt battery requirement as the Luna Pro SBC / Profisix and are of similar vintage:
A) Gossen Profiflash (Gossen Luna Pro F in the US); and
B) Gossen Lunalite - (Gossen Luna-lux in the US).
The Profiflash/Luna Pro F add the capacity for flash readings, but don't offer quite as much extended sensitivity for low light readings as the Profisix/Luna Pro SBC.
The Lunalite/Luna-lux replace the excellent needle based nul reading system of the Profisix/Luna Pro SBC and Profiflash/Luna Pro F with a small number of LEDs. They have less sensitivity then either of the others.
Those meters were successors to the earlier line:
a) Gossen Lunasix in most of the world (Gossen Luna Pro in the US); followed by
b) Gossen Lunasix 3 in most of the world (Gossen Luna Pro 3 in the US); followed by
c) Gossen Lunasix 3s in most of the world (Gossen Luna Pro 3s in the US).
The Lunasix/Luna Pro meters are not without their advantages, but they are older and they require a work around due to the unavailability of the mercury batteries they were designed for.
There are a number of accessories that add capabilities to many of these meters - some require the electrical connections of the Profisix et al, while others work as well with the non-electrical connection equipped Lunasix meters. At one time I had the flash metering attachment for the Profisix. I still have a semi-spot attachment and an enlarger metering attachment, both of which will work with both the Luna Pro F and the Lunasix 3s.
I used a Profisix for several decades and was very happy with it. I now use, in order of frequency of use:
I) a Gossen Digiflash;
II) a Gossen Luna Pro F; and
III) a Gossen Lunasix 3s.
My old Profisix and my current Digiflash were bought new, while the Luna Pro F and Lunasix 3s were bought used.