The BG Pro's grip is big and comfortable enough to counterbalance a fairly weighty lens when shooting handheld.
Because the lens images upside-down, you need to use software that can flip it. Or shoot that way.
The rig consists of two pieces, and the separate DOF (depth-of-field) Adapter is a few pieces itself.
There are two standard 1/4"-20 screw mounts on either side.
This is what the rig looks like assembled but waiting for a phone, and with the macro lens in the mount.
The grip on the BG Pro equipped with the DOF Adapter.
The bottom of the right half of the rig.
If you just want a substantial grip for holding the phone to shoot handheld, you can use the right side by itself.
A spring-loaded clamp holds the phone in place. You can also tweak the location of the jaws by moving them to adjacent screw holes.
The Adapter awaiting a lens.
The rig with the DOF Adapter, from the left.
There are three 1/4"-20 mounts on the bottom.
The BG Pro with an iPhone 6 Plus in it.
The view from the front, with the 10x close-up lens.
The two rails slide into the right half and you secure them with two thumbscrews.
The naked lens mount. It has brass threads.
The DOF Adapter has a Canon EF mount.
The focusing screen sits between two other rings, and making sure that it's level as you rotate all the different tubes can be trying at times.
From left to right, the Adapter consists of a 10x macro 37mm-to-52mm converter, focusing screen sandwiched between two rings, and the EF mount tube. A 37mm 10x close-up lens goes on the mount between them.