For technical reasons I do not recommend these aluminum blocks!
The Brompton block in industrial plastic is much wider than the threaded rod brazed on the bike head tube and its material has some elasticity.
When it is attached on the bike, its sides are pressed against the bike head tube what provides an excellent lateral stability.
The aluminum block are narrow and only hold on the brazed rod they do not touch the bike head tube at all, their lateral stability rely only on the two bolds and their thin sides.
They are definitely not good for heavy load or wide bags (some brands are honest and specify a max load lower than the 10kg allowed by the Brompton block).