Its a decent overview from a CSX perspective, who (along with NS) has only really started to use it.
CSX has had DP capable AC motors for sometime, but rarely used it. The cost with new locomotives isn't that much greater, especially since GE bought Locotrol moons ago.
Couple of things that can be explained...
DPU wasn't to eliminate crews, but became a byproduct in the last few years with improvement in the DPU software and communications link. There is a practical limit (without using repeaters) of about 8500' between the consists for most trains, with western railroads limiting around 10,000 with intermodal trains. For longer trains that are EngXDPxEOT, 15,000+ ft trains are possible - depending on the territory and territory limits.
Locotrol/DPU has actually been around since the early 1960's, Southern Pacific experimented with it in the central valley region. IIRC, Westinghouse initially provided the equipment.
In the 1970's, Harris came up with Locotrol, and they were referred to as master/slave units. SP purchased quite a few and due to technology at the time, EMD extended the nose of the engines to accommodate it.
Clarification of what he stated (but accurate for CSX), Locotrol was available on DC units, and did not require computers. Commonly known as a "Harris Box", it was a box similar in size to the Head of Train Device (for the EOT's) that had a simple LCD/dot matrix screen.
Every AC unit by GE and EMD today are computer screen based controls and Locotrol (if equipped) are integrated into such screens. In fact, if Trip Optimizer or LEADER is present in the locomotive, it will put of the fence (see below) and run the different consists as the computer thinks it should. This happens with the standalone programs or with them integrated into PTC.
An additional clarification, the remote unit do not always "mirror" (commonly known as 'synced'). It is also not difficult or uncommon operate them when making setouts or pickups. There is a simple command called "setout function", which will cause the DP units to ignore commands. Also there is a command, commonly known as "using the fence" (or "move back/move front") that puts up a barrier between the controlling engine and any remote units. It lets you control the DP's independently. Currently you can have up to 5 remote DP consists, but only one fence, if you use it. Most railroad rules require the fence used and the DP
s in a higher throttle setting when starting a train, kept them pushing over a grade while the head is in dynamics, or any other territory specific setting.
It is true that brakes and air work better, as well as entrain forces. However when they are made stupid long, the air and brake issues return just based on length and leakage. Train makeup also plays a role as what kind of cars and/or loads empties in respect to their position in the train (as well as hazmat placement).
Back to more modern times, Harris used Motorola Spectra radios as the core for the transmitter and receiver. With narrowbanding and the end of life of the Spectra's, Kenwood cores are now commonly used. They are all headless, and use the controlhead data interface to the Locotrol computer.