I have a long neck as well and I am 6 feet tall. I have tried both the Kun and the Bon Musica. I prefer the Kun, but it’s not perfect. I still have to lift my shoulder a little. The reason I did not like the BonMusica is because the padding is not as thick as the Kun, thus it cuts into the shoulder a little.
I am about to try the Wolf Forte Primo Violin Shoulder Rest Violin and see if it works better. Details to follow soon..