Initially we just went with what we found online. So at first the reactor grid was just a grid of buttons, but that turned out to be quite slow (creating the buttons, changing their colors via stylesheet changes, etc). It also didn’t have a way to zoom the whole thing. Then came the Googling, from what I found most of the new stuff (QtQuick, QML) is presumably slower than Stylesheets which in turn are slower than a QGraphicsView. Unfortunately, this also doesn’t work very well (make a large grid, it’ll lag a bit); this seems to be to some extent related to Python and to some to the CPU rendering that Qt defaults to. While it is possible to implement OpenGL rendering with not too much work, we have not yet bothered to do so, particularly because it’s not clear if there will be much benefit (we’d have to rewrite the paint events which would cause extra python function calls which as we know are disturbingly expensive). So it would reduce the rendering load but possibly just add even more as a result of function call overhead, so… not very enticing.
In general, at least for my part, I don’t think I can say much about Qt from this, since I suspect most of the issues I had with it (this time around) are related to Python (and PyQt). I would have to try it in C++, but that’s even less portable than Python so definitely not for this. And I’m not very excited about it for any other projects, I tried once a few years back and the open file dialog caused my Linux kernel to crash in such a spectacular way it didn’t post any error messages, it just froze. I had to hard reset the computer. And it did this consistently. 
P.S.: Why does butt automatically link to Wikipedia?
P.P.S.: Anyway, figure out some good designs with as high an efficiency as possible (without using Thorium salts as a coolant, or IC2 for that matter) and post them here! Maybe we could make a contest, best U238 only design, best U235 etc? 