Well, I would still suggest that it depends on how you do the split. Wally Shaw is a very respected and experienced beekeeper who has done a lot of research on a modification of the Snelgrove split. If you look at his presentation, you will see that he describes standard split methods as having a poor success rate at swarm prevention = 50% or less. However, the modified Snelgrove is much better than this. He has a success rate of over 90% in preventing swarming by using this method.
However, your success rate will definitely depend on diligent inspection timing, careful searching for queen cells, and following his description to the letter: