I'm jumping into this a bit later than I normally would, but I don't normally read this forum, despite the fact that I should.
I have the DMX Operator. So, I know how it work quite well. I can't say I know it 100% inside and out, but I can get around it quite easily. I need to refer to the manual for programming it because I can't recall those steps. Other than that, the DMX Operator is my buddy. It is my reliable fall back for MyDMX.
Issue 1: The scanner buttons.
Each scanner buttonis really saying "activate this bank of 16 DMX channels", not necessarily a scanner. Many people do use it with a scanner button controlling a specific scanner or type of scanners or groupings of scanners. Not me, I look at it as pre channels, but I also logically address my fixtures so they can be controlled easily. To each their own, whatever works best for you is the right way to do it.
So, let's say you hit scanner buttons 1, 3 and 5. You just activated channesl 1-16, 33-48 and 65-82.(assuming I did my math right in my head, do check me!). All other channels will be OFF/not used.
With a scanner button or buttons ON, and you move the corresponding fader(s), all activated channels associated with that fader will be affected. In those regards, your assumption is 100% accurate.
In programming mode, the DMX Operator behaves MUCH differently. It does make sense, but it helps to have something plugged in, sucha as a dimmer pack(or packs) in case you can't really set up your lights when designing your scenes and chases. I'm not saying this is a negative, it's just something you should be prepared for.
When programming scenes, it is best to do this one scanner button at a time, or at least matching like for like channels/fixtures.
Let's say your first 8 channels are banks of ParCans. Your second set of 8 channels(9-16) are "high tech effects. That covers scanner button one. When you are done making those settings for scanner 1, you turn it off and then go onto Scanner 2. Let's say on Scanner 2 you have color wash fixtures that use 7 channels, and you have one type using 17-24 and another type using 25-32. Again, after you make those adjustments, you turn off that scanner button. If you do pay attention to what you are doing and if you have the luxury of some sort of sanity check(say, actually having the lights set up or dimmer packs as place holders), you can se that things are turning on and off according to the scanner buttons. But if you save and recall the scene, you'll see that all your settings are saved.
In stores, there is too much stuff coming out all the time. For example, Guitar Center carries ADJ, Chauvet, Martin and some new generic company that looks like they are making cheap ADJ and Chauvet knock-offs. Not to defend the store sales people, but there is so much product out there that it is not practical or really possible to know it all. With lighting fixtures, it can be a bit easier getting an idea of it based on the manual and specs page. Wiht a controller, it's not so simple. For example, on the surface, the DMX Operator doesn't look like much. And maybe it isn't, but I still love mine. It looks like a simple yet easy to use controller, and it is that and it does it very very well. This controller I have had since late 2001 and I still haven't fully utilized it yet. Once you get past the overly simplistic design and really dig into the short manual, you begin to understand that ADJ/Elation pack a lot of functionality and features into a very convenient and easy to use package. While you may think "wow, that's a lot of money" on an up-front purchase, but when you really start to utilize this controller, the value really becomes apparent.
In the data communications and computer world, it's rare to find stuff that is meant to be around for 7 years because technology moves so fast. Entertainment is matching that speed and in some cases, faster. Despite this, controllers haven't had to change a whole lot. Why? Well, certain things don't change, such as DMX signalling. So, we're not doing DMX-512 over IP or over UTP or fiber(or at least not quite yet). Good controller design is good controller design. Period.
Another option for about the same money might be MyDMX software. With the 3D Visualizer, that might give you better programming capabilities since you can see what you're doing easier. But I can't say a controller is a bad thing, it can also serve as fail-over in case MyDMX gives you some headaches at an event.
To the DMX protocol. It is continuous controller data. Why? Failure recovering I think. should something fail and get swapped out or need to be reset, it can then recover because it's instructions are continuously being resent. This is unlike MIDI, which while it does have continuous controllers, most of it is note on/off and other intermittant signals.
The best way to learn DMX is to simply get into it and start doing. Buy lights that do what you need and figure out how you want to control it. My words of advice: When it comes to controllers, buy something good and maybe above what you think you need now. In this case, my DMX Operator is on the lower end of things, but as I've said, it puts a lot in a small package. It's a good all around controller.
And, the DMX Operator really shines in scene mode. Design and document your shows and have fun.