His ability is actually awesome:
Whenever Scrap Trawler or another artifact you control is put into a graveyard from the battlefield, return to your hand target artifact card in your graveyard with lesser converted mana cost.
Just on his own, Scrap Trawler can get back a two-mana, one-mana, or zero-mana artifact. But the cool thing about the Trawler is that if you have any other artifact you control go to the graveyard, you can get back an artifact to your hand with a lesser converted mana cost than that particular artifact. To be honest, there are a lot more decks that could play this ability, and just haven’t. Or they just haven’t been competitive enough to break into the Modern scene. There’s even the rogue Legacy deck that plays him, and why not? He gets back your Black Lotus in Vintage, too…
In mid-2018, Scrap Trawler was pushing a $1.50 market price when its still been a $1 or less card just showed how much people stocked up on playsets of this guy. But Krark-Clan Ironworks decks, while they were good and certainly competitive, aren’t actually the reason this card had consistent demand. The real demand for this card is actually from Commander.
Besides three big artifact Commanders - Breya, Etherium Shaper, Daretti, Scrap Savant, and Glissa, the Traitor - there are plenty of other decks that like Scrap Trawler. Bosh, Iron Golem has been making a comeback lately and he loves this card. Even Depala, Pilot Exemplar decks can play it, to recycle Vehicles! Some Jhoira, Weatherlight Captain decks have taken a liking to Scrap Trawler, too. There’s a lot to like about this guy.
Scrap Trawler is a card that was designed to be a part of Vehicle decks, but that didn’t really happen outside of the occasional list. Still, you can be pretty confident that this is going to be a sweet long-term investment. He did push $2 for a time, before steadily dropping back towards $1. However, Scrap Trawler foils are about $3.50 as of this writing and that price is backed up by a similar market price. If another artifact-based deck becomes competitive in Modern, these foils could easily pass the $5 more and beyond. What’s his ceiling going to be? If he doesn’t get reprinted, which he may, who knows! Scrap Trawler foils look to be a decent investment going forward.