There are two versions of this puzzle, one of which is much more satisfying than the other.
In one version, all of the consonants are printed in the grid. This is rather banal and can be repetitive. The compiler must take care to avoid alternatives.
In the better version, the puzzle is clued with the consonants, but the solver doesn't know where they occur. So, for example, if the clue to one across is MN (4), the answer could be AMEN, MOAN, MEAN, MIEN, MOON, MENU etc. This is just as prone to alternatives, but it is more fun to solve.