Board Thread:Questions and Answers/@comment-82.10.67.67-20130405172124/@comment-326330-20130427094411

82.10.67.67 wrote: Can mobs spawn on these? I think they would make a good alternative to water in a grinder. They are an excellent alternative indeed; but as stated, mobs cannot spawn directly on them. You can't plaster the floor with them. However, if they are placed in the same way that a water conveyor would be, they will easily drag the mobs that wander onto them.

As far as I can tell, they're stronger (even a player cannot move against the stream, unlike in flowing water), more compact (they don't need a lowered channel, and can drag spiders even with a single-block width), and have no length limit.