Hi Adrian,
I'll be biased here and say
Ostahowski.
If your budget is tight, the GSO serves its purpose, the option is that you can always upgrade in the years to come. IMO, if your going to spend the bucks on an SDM why not go the whole distance and go with the premium optics.
Each to there own, but this is one vote for a T.O mirror.
I have no issues with mine.
Cheers Norm
PS: have you tried contacting Mark Sutching for a price - superb mirrors from an Australian.