That cord from REI looks a lot like some stuff that can be found at Walmart in the boating/recreation department. It's a braided line that comes in green, orange, or white. And it works great. I used it extensively for ridgeline and prussiks until just a few days ago when I swapped it out for Zing-it to reduce my pack size a bit.
As for braided Mason's line - the stuff I got at Lowe's has a breaking strength of around 80-100 lbs. Should be plenty strong for prussiks.
"...With saddle and pack, by paddle and track, let's go to the land of beyond."