"Marc" -- generally pronounced WITHOUT the final "c" -- is similar to, but NOT the same as, Italian grappa. Both are distillates produced from the pomace of the fermenting must (i.e.: the solids, primarily grape skins, after the wines has been drawn of and the must has been pressed).
While there are some notable exceptions, most grappa is bottled with little or no aging. Many grappas today are also bottled by their grape variety (e.g.: Picolit, Nebbiolo, Muscat, etc.), though some is still bottled by its original DOC/DOCG (e.g.: Brunello di Montalcino, Barolo, Barbaresco, etc.).
Most French marc are aged, and very few (I canot think of any, off the top of my head) are bottled by variety. Perrier-Jouët produces a Marc de Champagne, for example. The Domaine de la Romané-Conti and the Comte de Vogüé both offer a Marc de Bourgogne, and so on.
You ask: "Is it worth tasting?" Personally, I think ANYTHING is worth tasting!
"Is it worth buying," is another question. My advice would be DON'T. Good French Marc is VERY expensive. Better to buy a glass in a restaurant after dinner than to buy an entire bottle of very pricey stuff, only to find out you don't like it . . . .