I got my black engraved PBT keycaps from qtan. The caps will fit on any MX board, so you'll be okay. Not sure about the Leopold though; if you have that board, you might want to ask around. Boards with Costar stabilizers (like Filco, Das, CM) should be fine. As far as the caps go, they're pretty high quality; I love the rough texture and the way they sound. Makes typing on the keyboard a lot more enjoyable.
Recently I purchased MagicMeatball's set of thick blank PBT caps from imsto. I like these a lot better because of the otaku look, lower profile, and muted sound in comparison to the engraved PBT caps from qtan.
Profile refers to the height of the keys. The engraved caps from qtan have a standard profile, which is stock Filco/Das/Ducky height. The thick blank PBT caps from imsto have a Cherry profile, which sits a little bit lower.
I commend you for investing in a quality set of keycaps; they'll make your typing experience much more enjoyable.
Enjoy and hope this helped!