Answer:
You can set a cab in this Gemtite, especially a drusy. However, for an opal cab I would recommend you use an actual cab Gemtite setting as the prongs will be better to hold your cab correctly. With the closed back, whichever one you use you can very carefully use a tiny dab of glue to hold the cab more securely in place. I haven't done that for any of my cab settings though, and I have not had a single problem with them holding just fine.
Gender: Female
Age: 55 to 64
Length of Ownership: 6 months
Level of Expertise: Advanced