Engine block drain

[BristolE30]

Hey zone

Going to do a Holts Speedflush later on my cooling system. They recommend to drain the engine block but on the Wiki here I noticed it said not to do that as it can dislodge things that may later block up pipes. Is this true?

Also found the screen shot below - is it true for a M10 engine that a lower rad hose should be cool? Or does this apply to a different engine?

Appreciate the help

1CB517CF-6D64-4393-86D0-BD257EF33731.jpeg