Been using it since before it was Ignition.
As Curly said, the documentation is a bit weak, but they're working on it.
Ignition, though, can do so much more than SCADA and HMI. You can get a feel for what people are doing over on IA's forum.
Been working on getting upgrade money (hardware and software). In trying to sell it to our plant manager, the conversion went something like:
Boss: So can you use it for inventory tacking?
Me: Yes.
Boss: How about generating work orders?
Me: Yep. Sure can.
Boss: We need to improve our PO Log.
Me: Well, since we can move it from an Excel spreadsheet to a database, that would be great. We can do that in Ignition.
Boss: What about...
Me: Let me save some time here. The only thing that limits us is imagination and will. Just like Green Lantern.