Like Al I've been testing the HC-3 for the last few weeks. Bottom line is that I love it.
The controller is smaller in all dimensions from the HC-2:
HC-3
Depth comparison:
Width comparison:
Height comparison:
The HC-3 is MUCH easier to hold than the HC-2. Not only because it is smaller, but also because of the case itself. The plastic used on the HC-3 is much more textured than before, and the edges have more of a hard angle rather than being super round (you can clearly see this in the last picture). The plastic on the case also feels much more sturdy.
The screen is slightly smaller (correction... It is not smaller, they are the same size), and set back into the case further. It feels better and is easier to manage with a thumb. The model I tested was the HC-3-Sun and it is very bright.
The four physical buttons are easy to use without looking. They can be customized between horn/direction/emergency stop/home. At this time there are no other options to put on those, though that may be added later. The two outer buttons turn the controller on. When the controller is turned off, it fully turns off, unlike the HC-2 that went into a sleep state. This is one reason why the batteries are able to last so much longer.
There is a single mini-USB port on the side for charging and file transfer. When plugged into the computer it will not charge, but it also will not use any battery power. So transferring files from the computer to the HC doesn't drain it. Space is double the HC-2b, as has been noted. Speed of transfer from computer to HC, and from HC to locomotive seems quicker to me but I did not time and compare it.
The knob is nicely done. The old knob was smooth spinning (as is the new one) but often would feel like it was spinning when it actually wasn't. I had this happen a lot when using my thumb to move it. The new knob has the rubber insert (I like the Railpro logo on it) and it solves that problem. The feedback while spinning the knob is great. I also like how it is smaller and sticks up further. Overall a much better feel to it.
Overall functionality is about the same compared to the HC-2/b with a few small differences. One of which is the controller settings menu. Now you scroll through different menu pages similar to the Locomotive settings page. Turning on the controller goes to a different splash page before going to the main menu screen.
The lanyard and swivel are great. The swivel is 360 degree and the lanyard is well-made. Of course you could always substitute one of your own. For me (6' 0") the Railpro lanyard was the right height.
Overall very pleased with it. I will need at least one or two more controllers, and they will for sure be the HC-3. I'll let my kids use the HC-2.
-Kevin