The SkyScanner BL102 is a 102mm (4”) f/6.3 Newtonian reflector with a focal length of 640mm. The primary mirror in this telescope is spherical, and not parabolic. With a long focal ratio, this would not be an issue. A 4.5” f/8 spherical mirror such as the one used in the Orion XT4.5 has a mirror which deviates from parabolic by far less than the Rayleigh criterion of ¼ wave. A 4” telescope needs to be f/7.1 or longer to achieve acceptably sharp images with a spherical mirror, or about 3” longer in focal length than the BL102. The BL102’s optics also do not undergo any kind of quality control and tend to have other issues with the figure of the primary mirror and the flatness (or lack thereof) of the secondary mirror. As such, these scopes do not achieve sharp images – while certainly usable at low power and better than Bird-Jones catadioptric Newtonians sold at a similar price, the BL102 simply doesn’t compare to what a good 4-5” Dobsonian can achieve in terms of sharpness. The optics can thankfully be collimated relatively easily and without tools, so you can definitely get the most possible out of them, but they’re still fundamentally flawed.