The first duel deck, Elves vs. Goblins (EVG), was introduced on November 16, 2007 as a way to allow Magic players to open new product and immediately be able to play against each other. Two 60-card decks were sold with very-balanced power levels. Although the decks themselves would never win any tournaments, there were usually a few cards that were useful to professional players and kitchen table mages alike.
After releasing the second duel deck, Jace vs. Chandra, a year later, WOTC would then subsequently release two duel decks per year for the next 9 years. Most were panned, as they were not remotely close to competitive, even at Friday Night Magic events. Players ended up pulling the one or two best cards out and dumping the rest.
A Japanese-language-only re-issue of the Jace vs. Chandra duel deck was released on December 3, 2010, with an MSRP of US$19.99. The reissue featured Jace Beleren and Chandra Nalaar with holographic foil treatment and anime-inspired alternate arts, illustrated by the Japanese manga artist Yoshino Himori. MTG Wiki
The last duel deck, Elves vs. Inventors, was released on April 6, 2018, bringing the franchise full circle to its elven beginnings. Duel decks were then replaced with Challenger Decks, which no longer sport their own expansion symbol (the cards use their original expansion symbols), thus rendering them non-unique and therefore non-collectible.
At first, I had thought that these duel decks were one-off products, so I opened them and put the cards in binders, not really expecting that some would later retail for $100+. With the Duel Deck Anthology, introduced on December 5, 2014, I was able to score sealed versions of the early sets (see above picture).