Yo;
   Mason is very strong, durable, thin, and comes in many bright, attractive colors.  It makes pretty good West Country Whipping except that it, being made from Nylon, is very slippery.  A solution is to use, instead of the normal Overhand Knot associated with WCW, use the Surgeon's Knot pictured below.  It's just an Overhand Knot with an extra pass through the loop.  This will hold it's place much better than the Overhand Knot while you're making the whipping.  Your finished product will look just as nice or better.  As you pull it tight you'll hear a faint "click," indicating that the knot has slightly locked and won't fall apart as you make the next one.  The Surgeon's Knot is helpful when using Mason Line or any other kind of slippery cord for West Country Whipping.

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I'd like to add that it's best to use the thinnest Mason Line available for WCW.  The thicker stuff just doesn't cover as neatly and evenly.  

I don't  whip my slings but I do use the surgeons knot to end stitching. I feel like it gives a better hold. I need to try a sling from mason's line. I keep hearing about it.

  Oh, yes, it's good for more than just whipping.   I've made several slings with mason line pouches (Eoraptor has one or maybe two.. I don't remember where the others are) and some with mason line braided into the cords with other materials.  It's colorful, very pliable, and stronger than perdition.   It makes a very good, very colorful, extremely strong, durable sling.  Try it, you'll like it.  At the Truck Stop where I buy some of my slinging supplies they sell small kits with like five different colors of mason line in varying thicknesses.  Good stuff!

I don't care for mason line as a sling material (too pliant, too slippery, too light), but it is amazing twine (though it absolutely has to have knots tied in cut ends, or it will untwist, like any nylon cord).  I've found heavy duty masons line (ordinary thickness, must be higher quality fibers or something) that had a max load of 160 lbs on the label.  I didn't believe it, and tied some to an overhead beam and put a foot loop in the bottom of it.  Sure enough, it could hold my (165lb) weight with only a little stretch, though it broke when I bounced a bit.  I've had somewhat poorer experiences with its abrasion resistance, but I haven't braided slings from it in at least 3 years, so I can't exactly remember.