They'd be pretty useless, and work out as horrendously expensive compared to Soviet AP mines (which should be at least 10 munitions IMO)
For 80 munitions you get a dozen (?) mine quadrants, which is actually pretty awesome. The trick is to make sure you have two Pioneer squads when laying them.
I think he means that you place 1 quadrant for 25 munitions, which will turn into 3 mines S-mines on completion.
On the subject of S-mines, I think all they need is the removal of the damn signs. Right now, if you hit a mine (or see the signs in advance), you can often just walk around the minefield. If there would be no signs, it would much harder to predict where the field is after you hit one of the mines, which would greatly increase the areal denial effect of the S-mines.