Yeah thats a really cool GUI.
Yeah today things are much easier. Juce handles a lot of the stuff that make the process of making a plug in very long. it handles the framework, libraries etc. Even the GUI, you can use some bundled knobs faders etc..
I did try a few times but when I actually got it working it only took me like a couple of hours getting it working. And Juce also offers a build in test system, so you can actually code in "real time" almost like using Axolotis editor, but just with VST's Its pretty cool .All though first one I did, I made it in Xcode. I need to get that set up, so I can do it "real time"
A lot of the big vendors use it too. I think Eventide makes the UI in Juce and a also Slate Digital for example. So its definately "professional standard".