The Pure is not so different to a Poker, it has one key more and if you want, additional backlighting. The keycaps are pad-printed and PBT when you choose the one without backlighting (with backlighting the keycaps are afaik transparent ABS with a black coat). I experience no PCB-flex at all which I heard can be a problem with the Poker?
In terms of customization, of course you can get custom keycaps for it, as for every keyboard with Cherry MX switches. It is PCB mounted by default, so could add a plate if you want, and of course a metal case (however, you can buy Pures with metal casings already installed). The cable is detachable so you can use a custom cable without the need to solder. So basically you can customize it as much as you want.
