I will have to check out Walmart - I use Fireline almost exclusively for anything other than plain stringing - I think I've worked through about 5 125 yd spools since I discovered it a few years ago!
Recently I was working on some really dainty earrings (from a pattern in the October issue of Beadwork) so I got out my Nymo (size D), because I was using delicas, 15's and 2 and 3 mm stone beads with multiple passes. Using the Nymo again for the first time in years, I really appreciate the Fireline - I don't need to pre-strech it, or use any beewax or other conditioner. I don't have to worry about splitting the thread (taking out a mistake in my right-angle-weave project finally involved the scissors!) and I can pull just as tight as I need to without it breaking.
I use mostly 6 # test, I also have 8# for any projects with heavy beads (like hematite) or seeds larger than 11.
In this recent project I also tried a 4 # test weight (brand name Stren, comes in a foresty green), but discovered it wouldn't go thru the size 13 needles very well.
Lori in NH