Cooler MasterCK351 Optical Gaming Keyboard (UK Layout) - Red Switches (Hot-Swappable), Full NKRO, Per-key RGB (MasterPlus+), Wrist Rest, Customisable Keycaps - Full-Sized, Wired, QWERTY

First off I was not specifically looking for an optical switch keyboard, but the price for the CK351 was good, and since I have enjoyed using an existing Cooler Master keyboard, it seemed like a good purchase!Initial impressions were very good. The optical Red switches are quite something to type on and to me the keyboard is visually attractive with excellent per-key illumination configurable by MasterPlus, CM's in house software or on the board itself using Fn key combinations.The keyboard is full UK layout. I realised a short time into typing that the |\ key (to the left of the Z here in the UK) was not working. It neither registered being pressed nor lit up.Since I am a techie I use this key a fair bit so this issue was not liveable.Support using CM's ticket system is quite lacking. I don't think the person trying to resolve the ticket understood the problem, perhaps not being familiar with the ISO UK layout.Since I couldn't find any support for this problem, I had to return the item. Of course this was smooth as Amazon is the seller.I then chose the Cooler Master CK550 V2 with Red Switches as a replacement. On this one all keys work fine... but the traditional red switched are not as smooth as the opticals on the ck351.I can't really speculate the reason for the key not working.... if I had a defective keyboard then others should be fine.... but the reason I chose a different model is that my gut-feel told me this could be a firmware bug and if it is, any like-for-like replacement would be similarly afflicted.