Yes. Backbone One is a form-fitting controller for your iPhone and to be a precision input device, it has to firmly hold on to your iPhone. As a result, you will need to remove other iPhone attachments (especially the protective cases that change the dimensions of your phone).
We designed Backbone One to avoid compromising on gameplay at all costs. We’re so confident in the improved experience of playing mobile games that Backbone One delivers, that we think players will be happy to remove their cases to enjoy Backbone’s benefits.