I've done some Mystery Quilts that I've been very pleased ... and some that were horrors!
My experiences have been that some do an incredible job of explaining what is the "right" fabric choices. Whereas some ruin the experience by not being able to give good guidance for that step. As a result, I've found that for those I ended up not being pleased, as the project did not come together at all.
Similarly, how well are the instructions written up? or if taking it IRL, the ability of the group leader to guide you through the stitching stage, to keep it enjoyable.
For sure, there is an element of risk in doing any Mystery Quilt. Will you like the overall design? Will you choose fabrics that play well together in what you make? What one person likes and thinks makes a great quilt, you may not like.
What you might want to do, is to check with others who have done a Mystery before via the same person (IRL or virtually) and find out how pleased/displeased they were. Ask to see the quilts (as you have here) that they have made. That will give you a good read as to how your experience might be.