I just completed a build with Box Royals. It's a TKC-1800, so it's a fairly flexible plastic case with a metal plate. I've currently only used sculpted SA keycaps on them. Also full disclosure: I am a clicky switch person, but I don't like clicky exclusively and do like to change things up occasionally.
My initial reaction is that they are not mind-blowing, but they are very "normal". I think this may be better than mind-blowing because they will be enjoyable for the long haul. They are definitely more tactile than Zealios, which disappointed me to be honest (this adjective clause modifies Zealios, not the entire preceding clause). The Box Royals have a sharp tactility akin to a heavy rubber dome but without the sponginess and short travel (BLASPHEMY); I don't consider this a bad thing.
They are a little bit heavy, but I prefer heavy switches (Buckling spring and Box Navies are my current favorites). They do seem to tire my fingers out a little bit, but I always get used to this after a while. This tiring effect could also be caused by SA keycaps on a keyboard that already feels large and spread out however. The tactility is more pronounced than Zealios and the sound is deeper and "thicker" sounding. The sound really reminds me more of a vintage keyboard. To those of you that like to type without bottoming out, you probably will not like these switches. It is barely possible to type without bottoming out; although that's never been my strong suit anyway.
I do need to try these with some other keycaps profiles, but, as of now, I think SA pairs nicely with them. Just as with Box Navies, the SA keycaps seem to take the edge off of the high weight and extreme tactility and put them in that "just right" category.
8.5/10
MY ONLY GRIPE IS THAT KAILH BOX SWITCHES NEED PCB MOUNTING LEGS! As I posted in another thread I had to do some PCB surgery because I'd soldered in the BACKSLASH key crooked (and subsequently lifted the pads and burnt the PCB trying to fix it). It took several attempts to get the switch straight because most plates are too open in that area to allow for ISO Enter and consequently do not support the BACKSLASH key very well; in this case, the PCB mount legs help immensely.