Wow - that is a great deal. It is basically just compost with a bit of lime. You might want to drive over and check out what they mean by "fresh" and "aged". All mushroom compost should be aged several months already because they are growing mushrooms on it.

The only issues I have with mushroom compost is it's highly alkaline, sometimes salynic and sterile as all get out. Basicly I'm saying it could do more harm than good to your microbe population. Occasionally it's also full of fungicide, too.

Greenjeans

Good feedback thanks.
My local SMS compost place says lime isn't added. Even if it is, that would be good as my soil is acidic at 5.7 ph. The compost is certified organic by the Organic Crop Improvement Association so fungicide shouldn't be an issue.
I may just get the fresh since it's so cheap and let it age myself, just in case it's too hot.

In my experience only if it's OMRI listed is it truly certified organic.

If it's truly an organic approved compost, they'll have laboratory test results showing AB, AF, TB, TF, as well as the chemistry. Ask them for the test results.

Also, ask yourself this: If it was capable of sustaining any kind of microbial life why wouldn't the mushroom grower have kept it? There's a reason it's so inexpensive and a reason it's referred to as "spent".

Greenjeans