Traditional pex piping is installed by slipping a metal ring over the exterior of the pipe, then slipping a union or any other joint inside and crimping the ring to hold it in place. It works, but given that its success lies in the installer doing a good job on crimping, there is room for error even if that is a small chance.
Uponor has developed a different technique for attaching fittings which incorporates the shape memory capability of their Pex-a tubing (not possible with Pex-b or c), so it can be stretched and it will return to its original shape. An Uponor pex ring is slipped over the tube, the tube is then stretched so that fittings larger than the inside diameter of the tube could be slipped inside. With a larger fitting inside, the tube is unable to completely shrink back to its original shape, thus creating an incredibly tight joint.
What is new here is not the Uponor PEX system, but Milwaukee's expander tool dedicated to it. Uponor originally launched hePEX and AquaPEX with a hand expander tool, and given the effort required to stretch tubes by hand, Uponor did not instantly wipe out the competition.
Pex expander tool © Milwaukee
Not long after that, Uponor developed a power expander which was a huge improvement over the hand tool, but still required significant effort. With the original power expander you had to remove the tool, rotate it, then put it back in and expand the tube further. Failure to rotate it would potentially leave channels that could cause leaks.
The big evolutionary leap came when Uponor partnered with Milwaukee to offer a better expander tool. While pex (crosslinked polyethylene) is the generic term, only Uponor brand pex tubing can be used with the Milwaukee tool. Uponor’s F1960 style fittings are slightly larger than conventional pex fittings and the tubing has an expansion and shape memory capability.
The tool Milwaukee came out with is about a quarter of the weight of the previous power expander and about a quarter the price as well. It also includes an auto-rotation function making it about four times faster to use, since you only insert and remove the tool one time. Below is a video of this thing in action. After trying it once you'll never want to go back to a pex crimper.