The peppers appear to be very happy in 100% mushroom soil beds. The tomatoes are growing a little slower than the ones in regular compost. Transplanted red onions are doing fine, and turnips, spinach and carrots have germinated in the mushroom soil.
The only questionable crop is the romaine lettuce. Usually it grows tall and compact, but the lettuces growing in 100% mushroom are very dark green and the leaves are spreading out on the ground instead of growing up. Will update.