The Matter Reshaper only costs 3 mana to cost, but one of those must be a true "colorless" mana. In Eldrazi decks, this is really never going to be a problem. His “when it dies” effect is also very powerful. When the Reshaper dies, you look at the top card of your deck. If it’s a permanent card that costs 3 mana or less, he puts it into play, including if it’s a land. If the card isn’t a permanent that costs 3 mana or less, you put it into your hand. Either way, he can easily replace himself by putting another card into play or another one in your hand.
Sure, if Matter Reshaper gets removed from play (exiled) by a removal effect like on Path to Exile or Swords to Plowshares, you won't get the ability. But, more often than not, you'll make sure that he dies. In any case, if he hits the graveyard, you will get something out of him, either way, which is important for keeping tempo.
The height of Matter Reshaper’s popularity was in February 2016, as Eldrazi decks were rampaging through the competitive Standard scene. In October, when cards from Oath of the Gatewatch were no longer eligible to be played, there was suddenly a huge supply available. As Modern isn’t nearly as popular as Standard when it comes to competition, his value has suffered over the years, making him one of the cheapest Magic the Gathering playable creatures out there.
This rare creature from Oath of the Gatewatch is probably one of the more underrated Eldrazi. Years on, he still sees a good amount of play in a variety of Modern and Legacy Eldrazi decks. As part of a smaller set that was opened a lot, there are a lot of copies out there. If you’re planning on playing Eldrazi any time in the future, this is a card you want a play-set of on-hand (four copies). Eldrazi is his best deck, obviously, and while that’s the only niche he really fits into, that's a highly competitive deck archetype that's not going anywhere.