This call populates an internal list of devices that are only accessible via API calls. There appears to be no way of searching through devices to determine which ones expose a specific primary service.
I propose two new API calls to address this use case
lb_result_t lb_get_bl_device_count(lb_context lb_ctx, int* device_count);
lb_result_t lb_get_bl_device(lb_context lb_ctx, int device_index, lb_bl_device** bl_device);