The Rovners are perfectly adequate ligatures, as long as they are a good fit for the mouthpiece. Try to use a standard for clarinet Rovner on a crystal mouthpiece (or on a standard size and taper German clarinet mouthpiece) however, and you will find that the Rovner is - um - "somewhat less than flexible".
The problems with the Rovner ligature on other that 100% standard clarinet mouthpieces, along with a chance encounter in the household accessories aisle of a Schnuck's supermarket, are what led me to design and perfect my Reedwrap ligature back in the 1980s. It offers the vibrational flexibility of a classic string ligature (the point of the Rovner as well) in a form that retains the shape of the mouthpiece/reed combination (the main problem with the classic string ligature), but in a configuration that allows it to fit an infinite variety of mouthpiece designs, tapers and materials (something that the Rovner, along with every other ligature on the market, including the woven string designs, just cannot do).
For that matter, the Reedwrap design goes one step further. If you purchase one long enough to accommodate (say) a contra-bass saxophone, you can use the same ligature on various single-reed mouthpieces all the way down to the Eb clarinet. (I never tested it with the Ab horn, but I imagine that it would be a bit cumbersome with all of that unused length wobbling around your chin - so, Ab clarinet players should stick with one custom made for their horn.)
In emergencies where someone's sax ligature broke at its single screw attachment point, I have fortunately been close at hand to rig them up with a spare Reedwrap from my clarinet case, no matter if the horn was a clarinet, an alto, tenor, or even a baritone sax. It's just that flexible (which is a pun upon its original, "as responsive as string" purpose). Try doing that with a Rovner and see how far it gets you.
I slacked off of marketing my invention (US Patent 4,796,507) when I moved down here and took up a management position (which cut into my ability to attend the annual conventions held by the ICS), but I still sell a few a year to teachers who got hooked on them early on. Of course the patent has since expired, so anyone wanting to produce same is more than welcome to try. Good luck with that