Yeah, complicated. I just learnt something new too. Ta astro-bot.
There really isn't any difference that you can do without actually testing each and every mirror. And, as an example, then you might find that a BK7 mirror might have a better figure than a Pyrex one, and then the difference in the material is only a cooling aspect, but once equalised there is no difference in performance. The vast majority of dobs from ANY of the brands listed in this thread will give a very good image.
The differences in material are not important. Really they are not. For being mass produced, the average quality of any of these is very, very good. Yes, every now and then one will be poor, and another exceptional, but this has nothing to do with one being Pyrex or BK7. What they ALL have as a common flaw is the particle board mount that they all use. These eventually fall victim to dew. But there are steps that can be taken to slow this from happening.
Like Allan said, I too would preference a GSO scope (Bintel falls in this case too) for the better standard focuser they use. GSO scopes also tend to be better priced too. The two main retailers of GSO scopes are
Bintel and
Andrews Communications. The service provided and knowledge of both retailers is excellent. I have never had a problem they couldn't resolve for me, and these have been very rare.
At Katoomba we can have anywhere from 10 people to 20 people showing up. Enough numbers for you?