My 6" f/5 Mak Newt has a 32% central obstruction, so I seriously doubt that the f/5.3 has a 20% obstruction. It's even difficult to find standard commercial Newtonian's with central obstructions less than 25%.
MNs designed for visual usage place focus very close to the tube wall, squeaking by with as small a (fully illuminated) secondary as possible. Placing focus so close to the OTA presents a dilemma for imaging and bino-viewing though, usually requiring a relay lens (or Barlow/Powermate etc) to sufficiently "draw out" the image enough to reach focus. To accommodate these uses, some later designs bumped focus further from the tube by reducing the distance from the primary, necessitating the use of a larger secondary, hence a larger CO.
While nice images can be attained using a MN, its greatest prowess (IMHO) is attained when optimized for visual use.
PS: I loved my (visually optimized) MN86 but, alas, eventually parted with it to make room for other equipment (it was built like a tank, and almost as pretty!)
My Mak Newt 8" f 6 has a 17% central obstruction and it weight less than 12 kg.
My 8" f/4 has a 25% CO and weighs about 22lb (10 kg).
Just to join the party, here's my MN-66:
Quartz primary, clear polished on the back to speed up cool down, 20% CO, 1/50 RMS , 1/10 wave certified by Intes. Mount by 1st Base Mounts, assembled and finshed by yours truly.
Unlike other MN-66s, it has a fan on the side sticking out like an ugly wart, but which also helps clearing off the boundary layer from the primary. In addition, the mirror is cored to hold it to the cell with a plug/nut.
After I almost broke my neck in the dark trying to use it on the CGE, I put it on a dob mount where it excels in both widefield (2 degrees with a 23mm Nagler clone) and planetary usage (300x on the planets and 500x on the moon). I've used it a lot more since I put it on the dob mount simply because it's always ready to go and cools down in 30min.