Hi,
Sorry to hear about your disappointment with the 450p & thanks for posting your review. If the spacings are incorrect for the altitude bearings to run true, then I'd suggest contacting the supplier and reporting this (along with your other findings). It may be important to do so before attempting mods - in case you are ultimately not satisfied ... it's a lot of money.
I had looked long and hard at this scope on the web a year and a half ago, and had been very tempted! I would have expected better from Skywatcher tbh. Personally, I thought it a good looking scope; and with the size of those alt bearings, had hoped it was a sign that care was being taken in the design to ensure smooth motions and balance. These are really key to the enjoyable use of a manual dob.
That mirror cover looks flimsy - if I remember correctly, someone reported the foam detaching and flopping down on the edge of the mirror - leaving a residue on the mirror surface. I see it coming away in your pic - watch out for this so - no one wants to have to clean glue gunk off a brand new mirror!!
Re Andromeda, I see 2 dark dust lanes in my 250px when cooled, collimated and dark adapted on a decent night. You need a large fov for Andromeda - what EP were you using?
Best of luck, and keep us posted on how things go with the scope,
-Niall