Re optical quality in general, it depends on how fussy you are I guess. Quality of the optics varies a bit from scope to scope. Last week we star tested two 12" GSO Dobs side by side both purchased within the past 6 months. One clearly had a better mirror: defocused star image showed rings of more closely uniform brightness, the other (mine
) showed inner 3 rings much darker, which I believe indicates spherical aberration (undercorrection).
I don't know how Synta and GSO optics compare. The Saxons (e.g. from AOE) and GSO look-alikes (?) sold by a dealer in QLD (?) are the only mass-produced Dobs I've seen around that use pyrex mirrors. Might be worth the extra cost for your climate.