It's basically a license for a tiny hardware startup to do Qt development with some limited support. It's not a very good license to sell product with, since any hardware startup that intends to use Qt in a product will pre-negotiate the distribution licenses up-front to capture the cost in the BOM for a unit. The only thing this does is allows you to ramp your commercial license costs as you get closer to profitability.

Basically if I'm a hardware company A, and I want to build a device that uses Qt5, originally I would buy a commercial license up-front for like 5 figures. If I'm building this product using my own personal funds and not VC-funding then this represents a huge outlay to get commercial support. What this $500 fee does is allows me to do commercial-licensed development out of the gate but without any support resources beyond installation(which was easy). Then, when I start doing design verification and am fixing bugs in the product I can start paying for a full commercial license and get support if I discover an issue with the graphics engine.

Getting Qt up and running can be difficult if you've never done any open-source or Linux development before. And for some systems, having installation support is paramount because the build systems are not tightly integrated with Qt's build system(EG QNX). So it can ease some difficulties in using Qt.

I think this is a pretty good offering for a niche of users who would otherwise avoid all the GPLv3 code and stick to Qt core, develop alternatives to all the good Qt modules like the virtual keyboards and stuff, and then determine they don't need to pay for a full commercial license once they get up and running. This provides an alternative path for those users where they can feel comfortable just using Qt's version of certain things. And it's probably a big win for them.