Unprofessional I'm using the web app right now since the desktop one crashes with a nwjs bug. The only thing I'm missing from the deskop app is to save my projects as a project folder, maybe Ashley will implement it when he's got some spare time :P
On the other hand I've noticed the desktop app to be less resource-intensive (RAM-wise) especially when previewing big projects.
Regarding porting plugins it's kinda easy if you know what you're doing. I ported some and remade some things using in-built stuff. For some reason they removed some var thing and some C3 plugins like valery popovs's JS and others don't work anymore. I'd stay far away from plugins if I were you, unless you make small games with a plugin that works right now and never intend on updating it since some things just change so much it breaks half of them.
"give me an honest answer" if i'd feel like lying i'd go on reddit or something :D
About the browser interface I can't say I mind. In some cases it gets in the way (when Chrome has bugs), but then again in most actually I like it. I like having access to the dev tools and changing things like that damn dim whenever a popup opens, kills my eyes, so I can just remove it which is pretty damn awesome!
Another cool thing is that I could pick up a small project from my phone or whatever and the cross platform is again really great.
C3 has gone a long way since it was released, it's definitely worth it compare to C2, especially if you don't bother porting things. My advice is for you to finish whatever projects you have in C2 and then start new ones in C3.
gph.is/g/4o6Rz6K
(couldn't get the embed to work or I stupid)