This is a fun little throwaway trick that you can instantly do when someone finds out you're a magician and says "Hey, do a trick." The ring the spectator sees and handles is a normal ring, so they can inspect it as closely as they want and they'll never see a thing. There is, of course, a swap involved along the routine, but Jay's handling allows you to start and finish clean.
If you decide to do this on the spectator's finger, you'll just have to keep an eye on the angles. It can appear a miracle to them, but if a crowd is standing around you it's going to be a little tricky. There are a couple of moves you can implement that will allow you to do the trick surrounded, but it will make the way you're holding the ring look a little suspicious.
This is one of those effects that will really mess with the spectator's mind, but won't impress many magician friends. I should say though that the rings are top quality for the price. You won't be wearing them around town or anything, but they don't look like cheap plastic or something. It's a solid metal ring to the spectator, and it handles that way.
This is a great trick either as an opener or even solo for those "apparently impromptu" moments (that really aren't impromptu).