Have now tried this coupling style in two models.
1) Slightly more bulky than the hookes joint style they replaced.
2) Not as flexible, so installation requires slightly more room.
3) Quieter and less vibration.
4) By examininging the "spiral" cuts the coupling alignment can be assessed. If it is misaligned the spirals either tighten up or get wider.
5) Much to early to assess life.
On balance am satisfied and will retrofit other vessesl as their annual overhauls dictate.