I’ve got a 25”f5 obsession, I have a friend with an 18” f4.5, and regularly observe with another friend with a 28” Webster, who also owns a slew of very exotic and experimental modern dobs with large apertures. We all live in WA, so if you’re ever down in Perth send me a pm. I also use a 30” obsession up at the Perth Observatory and have been known to roll mine out alongside the 25” up at Gin Gin.
It always amuses me to read posts about having a large dob from people who don’t own one, so here’s my take.
These ‘older’ dobs have been operating continuously for over 20 years with no problems, take less time to set up than my previous portable scope - a newt on a German equatorial, and when fully motorised with a stellar at and Argo Navis will put a 17th magnitude galaxy right in the middle of the eyepiece. Do bear in mind that a ladder might be required to reach the eyepiece. Doesn’t worry me.
It holds collimation over the whole sky, can be easily setup by one person, and if you damage it, is made of easily sourced materials to replace or repair, and is still backed up by excellent support from David Kriege. I’ve seen a couple of SDMs and they are works of art at a premium, but do not do the job of holding two mirrors and an eyepiece in the correct place any better than the original Obsession.
Your decision should first be about quality of optics - all of the premium mirror makers should be able to give you an interferogram, and what premium you’re willing to pay for ‘bling’.
Cheers, and despite the claims from some people who are unwilling to accept physics, a good quality large aperture scope will deliver better views of everything under any conditions. Must be why there aren’t too many overpriced drinking straws in the Atacama Desert or on Mauna Kea...
Cheers
Andrew.