[datahipster]

Qt's licensing for commercial products is something like $500/month/developer. For a small team of 6 developers, that's $36k in licensing a year. Unfortunately, you're not allowed to take existing Qt code and "port" it over to the commercial license -- you're required to start from scratch IIRC.

[pknopf]

You can use the open source version of Qt with LGPL for commercial products.

[copperx]

Does QT use the latest C++ standards? Or do you have to adhere to old conventions?

[johannes1234321]

Qt itself puts lots of effort on compatible APIs. Therefore they don't fully push "modern" APIs. However internally they use a lot of modern C++ and enable many modern things in different small steps. For a C++14/17 purist it will still be "ugly", though.