Hydrangea macrophylla Lets Dance™ Rhythmic Blue 'SMHMES14' was selected by Timothy D. Wood of Spring Meadow Nursery in Michigan (PP25836, 2015). It's patented as new and distinct. According to the patent, "its upright, outwardly spreading and mounded plant habit; strong and sturdy dark brown-colored stems; early flowering habit; large mophead-type inflorescences with large sterile flowers; sterile flowers dark pink or blue in color depending on aluminum sulfate treatments; and good winter hardiness."
How new and distinct is it? In reality, most new and old cultivars of big leaf hydrangeas are upright & outwardly spreading & mounding, have stems of color, flower between early and late, have mopped or lacecap type inflorescences, have flowers that are pink or blue depending on soil pH, and have some degree winter hardiness.
'SMHMES14' is an open-pollinated seedling of Hydrangea macrophylla 'Bailmer' (aka Endless Summer®). The unique trait of 'Bailmer' is that it is remontant or re-blooming. Specifically, it blooms on old and new wood whereas most older big leaf cultivars bloom on old wood only. So, if you have a harsh winter or late spring frost that damages buds on old wood, a remontant hydrangea will still flower on new wood in late summer (probably not the stellar display that you wanted, but something). This trait is related to winter hardiness, but it is not exactly winter hardiness. To me, winter hardiness is the winter temperature that a plant can withstand without dying. This trait is only dealing with buds, as in "this Buds for you".
Getting back to Lets Dance™ Rhythmic Blue, it seems to me that its strong & sturdy dark brown stems (inflorescences do not flop) and winter hardiness sets it apart from other cultivars.