User JINKS did a photo comparison of 3 bags in post 185 of this thread including a wilserbrewer bag, an LD Carlson bag, and a paint strainer.
The wilser bag appears to be about twice as fine mesh as the LD bag with much heavier stitching at the seams. The finer weave produces clearer wort and much easier cleaning of the bag as grain bits do not get lodged in the mesh.
Advantages IMHO are:
1. Finer mesh yields clearer wort with less trub.
2. Much more durable
3. Much stronger seams for large grain bills.
4. Draw string w cord lock to fix bag on kettle while mashing, and closing drawstring during removal for less spills.
5. Custom size to fit kettle and resulting ease of use.
6. Optional pulley.
Of course a custom bag comes at a price, but long term performance may likely result in lower cost per use.
Ok, that's the end of my obviously biased report
Cheers and thanks,
wilser