Yes, I know that, and in my previous reply I even said I have seen people produce some great images with a Dob platform. But, I also said it depends on how much patience and dedication you have to mess with it.
How long can you go before you have to reset? Every 15 to 20 degrees, some even less, compared to my EQ mount that I can start level at 0° and allow it to go past 90° beyond the Meridian before I have to flip it. More time on target without having to worry about tedious BS. When it comes to astroimaging time on target is important to some of us.
No matter what anyone says, you cannot beat a EQ mount for astrophotography. By the time you waist your money for some of those Dob Platforms you may as well have invested your money in a EQ mount anyways.
I guess it depends on how foolish a person wants to be with their money.
You can get a nice Losmandy GM 8 for $1300.00 compared to $1750.00 for a dual axis platform that can handle the same weight. And for some reason I'll just bet that Losmandy EQ mount will out-perform that Dob platform, especially for astrophotography.
If a person is truly interested in astroimaging, at those prices I am sure people should be able to find a nice EQ mount that can be properly polar align and won't have to be reset after 20° of motion.
Have I ever used a Dob platform? No! I wouldn't own one.
Have I ever seen one in use? Yes! and that is what convinced me to never own one.
Dob platforms are all hype!
The purpose of a Dob is to make the larger Newtonian Reflectors more affordable with a stable durable and easy to use alt-az platform. Spending more money for a tracking platform defeats that purpose and compromises the stability. At least the one I saw wasn't exactly stable when it was leaning in one direction or the other. They Do Not Make the best platform for astrophotography, however can make observing easier.
Rather than spending hundreds, possibly more than a thousand dollars for a Dob Tracking platform save your money and build your own if you really must have one, for observing. You can find plans to build them with a simple google search.