I started this as a new thread even though there are others related, but I do not seem to have found anyone talking about what amounts to an add on set for Ninja+, which is made by Matthew Garrett.

He makes a set of four rings (11.5cm/4.5 inches in diameter) and they sell for $42.00/USD. Has anyone here seen or used these rings at all? If so, any reviews on them from users?

If they are any good perhaps these would satisfy the requirements of many magi as an alternative to the now hard-to-find Ogawa Ninja rings.