Ok, so measurements first -- I received 5 pieces in my mystery package. Each was a generous half yard, some pieces were wider but they were skewed -- still there was a solid 18" if I trimmed both sides down. Width was a consistent 44" usable. (picture 2)
I have done it before, but since I am doing product research I got a couple different color catchers, the Shout and Carbona versions and put those in for the prewash. I prefer to wash my fabric along with other laundry, most of which should have been stable/non reactive to the color catchers. In the light load, there was no cast off. In the dark load, there was a tiny amount of cast off color. At least one of the t-shirts in there was a new wash, so hard to say. There was no noticeable color change between the washed and unwashed pieces.
There was a reasonable amount of fraying, it did not shred or otherwise loose character, nor was there noticeable shrinkage. (picture 1)
I grabbed some pieces of fabric from my current project to compare the back side. You can see the narrow selvedge Mega fabric. The rusty bottom piece I got this year from Shop Hopping, not sure of the maker. The weave and weight are almost identical to the Mega, but you can see the thick wide selvedge. The middle piece is a gold embellished Asian Hoffman print from 10-20 years ago. It is a similar weight as the Mega fabric, the weave and threads are slightly finer but not much. The top orange fabric is also recent from my Shop Hop. I feel it's weave and threads are similar to Kona cotton. Is slightly different feel/weight from the Mega but they can certainly work together. (picture 3)
Final report: I am satisfied with my purchase, and will put this fabric into general stash and use without reservations. The mushroom fabrics I may be able to use early next year. If you like a particular pattern, I'd say go ahead and get it, making sure you understand the scale of the design. Sadly for me, as we already know, other than research I am cheap and find it hard to buy fabric at full price from anywhere.
But this is my idea of fun. I've got my quilting group today and will drop by the post office and send a sample to Wesing -- we can get his take in a week or so