I meant the blank 87/84 sets, but those are by the same manufacturer and will be the same in thickness.
As far as negative reviews, I haven't heard anything really bad about them besides a complaint about the spacebar (can't test because I have a 6x, not a 6.25x, which will fit your Ducky), it seems to me like all the keycap gurus around here say that it's quite a good keycap, and certainly a steal at its price. It should fit your board just fine, and light should show through just fine.
As far as the caps that qtan is selling, they're good caps, but unless it's mentioned that they're thick PBT, they're almost always thin.
Honestly these keycaps are so cheap that even if you don't like them (they didn't sit on my capslock well) you can use 90% of the caps and it's not a loss.