I was using Mac OS Yosemite, and got an upgrade to OS X EI Capitan recently. I noticed that Airtel 4g ZTE dongle (Model MF825A) was not getting installed, nor device was getting detected. When I researched, lot of blog posts were suggesting to set csrutil disable and try, which didnt help in my case. Most of blog posts, speak about Huawei devices and much less on ZTE devices.
Found like there is a patch file to fix the issue, by which I could install the same device and connect. Please unzip the attachment, and run the Patch.dmg file. When it is asking to drag your package, open the Mac folder inside the airtel dongle in another window, and drag the Airtel 4G.mpkg to that text. Click on patch, and it will proceed with installation of Airtel dongle, which earlier was failing with error 'The installation failed. The installer could not install the software'.
Hope this saves some time for your troubleshooting part for Airtel dongle MF825A on OS X EI Capitan.