Product review (5 stars): Works great - but too abrasive.  Here is the fix...
I have been using a round bottomed wok on my Kenmore/Whirlpool stove -- the stove for which this wok ring is designed -- without much stability problem for years.  Then I decided to give this a try.  It works very well, and I have come to love it....

BUT there was a rough spot at the beginning of our relationship.  The heavy cast iron of this wok ring has a very abrasive surface; the roughness is equivalent to a coarse grinding pad. As I cooked and moved the wok around, the four prongs upon which the wok sits were grinding the surface of my beautiful carbon steel wok.  Other reviewers have noted this problem. Some scratching would not be a problem, but this was not just scratching.  It was really GRINDING the surface of the wok, and it was far too much to accept for long-term use.

My solution was to take out a file and smooth the the prongs that support the wok.  That made a big difference in the relationship; wok and ring are now mating happily.  If this is a problem for you too, do this: Coat the wok with a generous amount of cooking oil.  Then put it on the wok ring, move the wok around, and take it off.  Notice where the the wok rested on the four prongs of the wok ring by the oil stains left at the contact areas.  Take a file, and smooth these areas down.

It took about thirty minutes to file the contact areas smooth. My arm was sore at the end of the task.  But now my wok sits and moves well on the ring.  The ring does not grind the wok surface, though it does of course leave some normal scratching.

My five-star rating takes into account this simple modification.  Without the modification to smooth the ring prongs, I was reluctant to use this wok ring -- and I suppose that would be a three-star rating, at best.

And I will add a bonus suggestion.  The Whirlpool or Maytag stove burner for which this ring is designed works very well with a wok, with a slight modification.  This is probably also true for other stove models. The gas burners on this (and similar stoves) have a top flame diffusion plate, which is easily removed -- it simply lifts off.  On the high-output burner, one can take off the diffusion plate, light the gas jet (light it on LOW setting), and then cook on a jet flame that is PERFECT for wok cooking.

I have attached several photos to show this.  Is it safe to do this, you ask?  I have used it this way for years to cook on the wok, but it is not something suggested in the operation manual of the stove.  Give it a try, and use your own judgment. This provides a big gas jet flame, and you must be cautious when cooking with it.  And it works only on the high-output burner.

Look at the photos. The first photo shows the file, and the smoothed wok ring prong.  The second photo shows the gas flame on low with the diffusion plate removed.  The third photo is taken with the burner turned to high -- note that this is a big flame.  The fourth and last photo shows the wok sitting on the ring, with the gas jet turned on high.  This is perfect for wok cooking.