I tested the 9.7-inch iPad Pro with WiFi and cellular radios. This iPad includes Apple's embedded e-SIM, which will allow you to sign up with a variety of wireless carriers in the United States and in other countries.
There's also a slot for a nano-SIM. When I got the new iPad, I set it up on T-Mobile because that's the carrier that covers my home and office. However, you can choose one of the other major carriers. The setup software allows you to sign up for a data plan while you're configuring the iPad, so I chose T-Mobile's free data plan.
The cellular radio in the 9.7-inch iPad Pro supports GSM/Edge and CDMA EV-DO. It also supports UMTS/HSPA in three varieties and LTE Advanced with 23 bands. Previous iPads supported 20 or fewer bands of LTE. In tests with the larger iPad Pro, I found that the additional bands allow use of LTE in a number of countries outside the United States.
Working with the new iPad Pro, I discovered the smaller screen of the 9.7-inch iPad is far easier to use in the field than is its larger sibling. I used the smaller iPad on a series of assignments, including covering a talk by a Federal Communication commissioner, and using the onscreen keyboard with my thumbs was easy. By contrast, you'd need really long thumbs with the 12.9-inch iPad Pro, which made note-taking difficult and slow. The larger keyboard, however, made actual typing easier.
Other types of field use argue for the 9.7-inch iPad Pro. It's far more portable, but it's still large enough to be useful. If you're working on a photography project, for example, the SD card attachment means you can view your photos on a large screen quickly. Likewise, the USB 3.0 attachment allows you to connect the iPad directly to many cameras. You also can use a card reader to look at images on the CF cards used by many professional cameras.
Even if you're not working with photography, those fabulous screens have their own advantages. I ordered some astronomy courses from The Great Courses, and the images that appear on the iPad Pro are remarkable. The combination of the screen on the 12.9-inch iPad and photos from the Hubble are far better than anything I've seen on any other tablet.
And therein lies the quandary. Which model is better, the more portable 9.7-inch iPad Pro or its larger companion the 12.9-inch version? In the office, the larger screen wins because portability isn't as important. But in the field, there's nothing like the 9.7-inch iPad Pro. Maybe the only realistic solution is to have one of each.
Fortunately, the 9.7-inch iPad Pro is about $200 cheaper than the larger version. It's also about that much more expensive than the iPad Air 2. Yes, it's a tough decision, but I believe the 9.7-inch iPad Pro is probably the best iPad ever, so the decision isn't as tough as it might be. And there's room in my briefcase for two iPads.