Some pieces require trilling on a B key which means you have to alternate B-C# really fast, and without a C# trill key, you would have to use your thumb and index finger simultaneously, which is hard! If a flute has a C# trill key, you would just trill a lever with your right hand's index finger effortlessly! Is it worth the extra money? Yes, if you have the money and if you play those pieces and make money with it. The rest of the blah blah below is AI generated just for the fun of it ;)

A C# trill on a flute is a musical technique in which the player rapidly alternates between the note C# and its neighboring note to create a rapid and rhythmic effect. The benefits of incorporating a C# trill into flute playing include adding variety and complexity to a musical piece, as well as showcasing the player's skill and dexterity. This technique is particularly useful in classical and contemporary music where fast and intricate passages are required. Flute players looking to expand their repertoire and challenge themselves would benefit from learning the C# trill, as it adds depth and interest to their performances. Additionally, composers may specifically notate C# trills in their music to create a specific sound or effect, making it essential for flute players to learn and master this technique.