I'm assuming he means this one.
Seems like quite a restrictive way to do it. It'll definitely be good to know how to do it this way, but I think in the long term, the way Kirjava explains
here is better, as you can check both the pieces that are in the UL and UR positions (both of which will be pieces that belong on the M slice) immediately before putting the pieces that belong in UL and UR in their place (the move after the M2 that solves them with respect to U layer corners). Based on checking both of those pieces, you can cancel into 4c by deciding whether to do U or U', while simultaneously being able to recognise the M-slice case (because you know what the BU sticker is). Hopefully that made sense.