One remark: you made the starting letter of each of these equal to that of the normal slider moving in the same direction (B, R, Q). This makes an easy mnemonics for the names, but is a bit catastrophic for the move notation and other places where a piece has to be identified by a single-letter ID. And I wonder how much the mnemonic is worth; these are only helpful if you already know the names, but are not sure which name belongs to which piece. But most people would not even be aware that pieces of this type exist at all.
One remark: you made the starting letter of each of these equal to that of the normal slider moving in the same direction (B, R, Q). This makes an easy mnemonics for the names, but is a bit catastrophic for the move notation and other places where a piece has to be identified by a single-letter ID. And I wonder how much the mnemonic is worth; these are only helpful if you already know the names, but are not sure which name belongs to which piece. But most people would not even be aware that pieces of this type exist at all.