The Field Test app's capabilities have been updated, but not its GUI. I'd been using the "Nokia Code" for over 20 years - starting on Nokia Symbian S40 and S60 handsets - in order to get optimized cell reception (voice and data) in remote job sites in the PNW - one of the last service challenges of cell phone service in the US. I'm from NY, and I'm pretty sure I can fit Delaware or Rhode Island in any of the remaining 20-odd holes in cell service around the PNW. The app can identify and quantify current data/information, data/information that the FT app couldn't detect even a year ago.
I know that the iPhone app's capabilities have been updated since it's able to quantify HSPDA-, LTE-, and CDMA-related data - I use both VZW and ATTWS handsets, and check for tower/antenna ID info and data capabilities at all of my job sites. In one project location (Wahkiakum County, WA), I was able to determine just last week the "voice" layers and "data" layers over LTE - the GUI of the Field Test app is irrelevant - It. Just. Works.