Hi Peter,
mate to IIS.
I had looked into getting a scope like this as large finder. One thing I found was that just about all 4.5" 1000mm scopes are 4.5" 500mm scopes with a very poor barlow lens shoved into the end of the draw tube of the focuser. CAUTION. Using another barlow in this case will only further deteoriate the potential image even further. You would be much better of getting a 4.5" 900mm scope. They too will be using spherical mirrors, but as mentioned, the problems posed by this mirror design is much less noticeable at this focal ratio.
These scopes are best suited as rich field telescopes, where, using a good eyepiece, they will be a joy to use.
I still have the instructions of my original 2" Tasco refractor from nearly 30 years ago. Then they did mention the 'maths' of telescopes & the practical limitations. Today these limitations seem to have been left by-the-by with many 'brands' in order to catch the unwary buyer.
Mental.