Used to use px12's, had a lot of issues with them releasing early (they had been checked). It was usually the worst when there was a lot of pressure in the tip of the skis. Had a few friends who had cracked the heels on their griffons, and I think I found pivot 14's for less than jesters, so I got the pivots. I love them, I have only released a few times, and while i can't say whether or not it saved my knee, it was always during a gnarly enough crash that I was alright with it. As far as weight, it feels like there is a little weight on your toes and heels, but when you swing the skis, they feel really light. Almost all the weight is concentrated right there so when I use them on my Bacon's for example, they feel super light.
Things to keep in mind. I was in HS when I had the PX12's, weighed anywhere from 150-170 (still use them as backup/summer/etc.). When I got the pivot 14's, I was probably 165, so it didn't make sense to pay more for the 18's. Now, I am between 185 and 205 (bulk/cut), and I still have the 14's. They still work great, but I'm at school in PA and not skiing a ton. If I were to buy new at my current size, I would get the 18's. They have an all metal toe, and they have no vertical release on the toe. To me, this is a bigger advantage over the DIN range. Obviously if you need your bindings that tight, really consider if you need it, then go for the 18's. I'm not going to be putting them that high in the near future, but those other features of the 18 would still be a benefit for someone like me. This is starting to ramble a bit, but I just wanted to highlight that there are many things that should be considered along with the DIN range.