Pros are bang for buck, simplicity, and comparatively easy DIY build (unless you get into really funky cabinets). Also have advantages for nearfield listening (hence their home in my office rig), and many designs work well with low power amplification.
Cons are, as you say lows; cabinet fixes, like transmission lines, can result in "tubby" bass. But my main complaint is different, I feel like I hear something awkward around the the transition to upper mids, highs.
My hunch is that many people will end up preferring multidriver designs, but I think single driver is a great thing to explore, esp. for DIY.
You might look at ZU speakers, too: a good company that uses big full range drivers.