The Morse key used on Titanic appears to be a standard Marconi Manipulating Key and would have comprised two keys on an ebonite base. The side key was a switch used to isolate the AC supply and the second key, the Morse key proper. The double exposed photograph taken through the window of the radio room on Olympic (?) shows what also appears to be such a key.
This style with two keys was very common in Marconi ship stations and various teaching colleges of the time and was still being used until the 1930s. On bigger installations, such as Titanic, Marconi also installed single and double magnetic keys to isolate the Wireless Operator from the high voltages which could be generated from the spark transmitters.
So the key itself is well known and I have seen examples at Radio Fairs in the UK. They look good when cleaned up and are well engineered and have a nice feel to them when used to send Morse. How much are they worth? I have seen them on sale at fairs for £80 - £100, but on Ebay with a few people believing that they are rare, who knows! There is quite a market for early wireless telegraphy equipment and the brass terminal pillars, and black ebonite bases make for a pleasing object to the eye.