This is the type of Pex-Al-Pex fittings I use.. you have to chamfer the plastic on the inside to make a smooth trasition over the 'O'-rings.. and it helps to have a 'rounding tool' something to make sure the pipe is round.. the compression nut is a good gauge for this.. I have a tool for inserting inside the tube to make is round.. I use a pocket knife or a large tapered reamer or a 1.5" drill bit to make the chamfer.
I like these because they are re-usable.. and if they leak, you can fix it often by tightening a bit more,, or remove the pex and add a thin layer of RTV on the O-rings and reinstall...
You may find a better price than this,, but it is about the going rate.. Greg L
Ebay::: http://cgi.ebay.com/1-PEX-AL-PEX-FITTIN ... 18Q2el1247
This link is broken, either the page no longer exists or there is some other issue like a typo.