My understanding is that we use "number" for discrete variables and
"amount" for continuous variables.

So you can say "The amount of flour required depends on..." or, "Last
night I consumed a large amount of beer!".

And, "That tank contains a large number of fish" or, "Over the week I
consumed a number of cases of beer."

I think that features are discrete, so the man page would read "...the
number of features will make your head spin!".