@FlyDragon One tip about ponds. We have two, a black one in our garden much like the one you are thinking of buying, and a green one at our allotment. You can see much more of the plants and the wildlife especially (damselfly larvae, snails, etc) in the green one. The black one is so dark that you can't see much below the surface.If this matters to you, if you have kids for example who want to see the critters, then try to find something paler for the pond material. You'll still see lots either way, but it does make a bit of a difference in our experience.
My mini pond is about 20 cm and it's shallow to be much use.