What's the advantage of PEX crimp/clamp over the expansion connection?
As I understand it, the expander only works on PEX-A tubing which is more expensive and not as durable/chemical resistant.  I have found that in many instances I had to make a connection in a tight space and needed the compact compression ring tool.  The expander has the advantage of working before the connection is made, so I suppose if you plan ahead you can avoid using the tool in a tight space, but the tool looks a bit more difficult to use in, say, a crawlspace where you'll be lugging around an extension cord everywhere you go.

Just my 2 cents.  I've never used an expander before.

Edit:
It also appears that contractors complain about the expander not working in cold conditions.