Mini Implants in the Maxillary Arch?

Joan, a dental implant patient, asks us:

From my research, I understand that the most prevalent and successful use of mini implants is to stabilize a lower denture.

From my most recent research, I have learned of the use of mini implants in the maxillary arch, to stabilize an upper denture. The cost quoted to me for 4 mini implants in either arch is roughly $2,000.

Though this appears to be a very reasonable price for the services listed, cost alone is not the main concern (for me). I wonder about the success/failure of mini implants for the maxillary arch? Is it an accepted procedure in this type of case or should mini implants only be used for a lower denture? Thanks for any comments or suggestions.