Zyex are a very good and interesting string from D'Addario. We find they are most commonly chosen by our bluegrass player clients, and have noted they were outstanding on a Kay bass - actually, the best match for a Kay bass we've heard to date. They offer lots of volume and a good pizz sound - similar to Obligato strings, but they seem to be more durable, which is a distinct advantage. Recently, we've heard some feedback that their arco response has been improved and they are being tried out by more arco players, and we have had orders for them for school basses as an upgrade from entry-level strings. It's a good consideration, as Zyex strings are quite durable.