I have ran and been around enough to feel comfortable with them and I have paid attention to them at IWF and AWFS. I think it is just like any other type or category of machine that gets popular, lots of companies get into making and selling them and they all have to be somewhat different. Just in the ones I have ran, there was a SCMI basic one, it was the size of a desk and the trimmer motors were Bosch hand grinder motors, complete with the cord plugged into an reg 110v outlet. It was made for the beginner and was cheap in the scheme of things. I have spent the most time on a mid sized HolzHer 1315 which is app 15 ft long and fairly well equipped, and now I have my own Adwood/Cehisa that is equivalent to the HolzHer in size and capacity.
The biggest thing about a bander is the fact that you have so many stations that do different things, these are machines that are harder to keep in trim than a molder or cnc router. There are at least 2 different types of glue application systems, either a glue pot or a cartridge. Then you have your knife to cut the banding, the pressure wheels - some are programmable and timed to apply at the right time. Next is top and bottom trimmers and rounding , then leading and trailing edge trimmers, maybe corner/end rounding, maybe buffing, scraping, heat guns, etc. There are so many options depending on what you specialize in.
Pvc banding jobs will want the end rounding, scrapers and buffers and heat gun. The solid wood strips, which can get up to 3/4" thick or deep depending how you look at it, you do not want any of those stations on when you run that, you have to change over to strips instead of rolls too, so you need a different feed wheel and turn off the knife. Veneer projects will be a combo in between these two. Some of them you can fill up the magazine with different banding and it can auto load it.
Then you get into the different controls on them, anything from none, just handles/cranks and manual on/off switches, to full blown cnc controls on them. That HolzHer was a PLC that you could program for different jobs and it would activate the needed stations from the control.
Next you get into the huge plants that their banders are a few hundred feet long and they get spun around, flipped etc enroute to the finish line. When you start adding in the material handling into them too, it gets real crazy.
Oh, I forgot about the premill stations too, if you get that, it will make a final finish cut to eliminate any chipping or out of whack saw cuts and give the best joint surface you can get before it puts the banding on.
So, take all these variables and figure up the different combinations you can get with them and it makes it a little easier to see why there are some many out there. Also take into account that they are the most finicky machine made and they can easily get kicked to the curb from disgust. If shops neglect them in the maintenance, it could get to the point very soon that it would be easier and cheaper to get a new one vs fix their pos.
As for curved parts, the only ones I have seen are various handheld or table mounted single station versions or Homag/BAZ makes a cnc router contour edgebander combo machine. They are in the $1.2M range. These are a pod and rail router that you put your blank of material on and cut the part and profile, then it will pull the banding from the loaded magazine and apply it, cut it to length and trim it all in one cycle. When it is done, the part just needs wiped off and sent to assembly.