Crew 1 on a 4/4 body is already a fair rate at three mana in a format where common creatures cap at 3/2 and 2/3, so the Van trades into the ground gum-up without dying to it. The doubler is what moves it from a body you tolerate to a P1P3-to-P1P5 pick in the colors that can feed it. The counter lands before the doubling, so a fresh pilot reaches 2 counters on the first attack, 6 on the second, and 14 on the third: each swing reads the full total, not just the counter it added, which is why the third connect is effectively a game-ender on the smallest legal Turtle, Ninja, or Mutant.
The type clause is almost never a real catch here. Those three creature types cover most of TMT's base, so off-type crewing is a choice, not a constraint. GU Turtles and a Ninja-leaning build want it highest, but for opposite reasons: GU wants a cheap pilot it can protect behind blockers and let the counters pile up, while a Ninja shell would rather hand the doubling to an evasive body and grind a single creature into a recurring two-for-one. Mardu Sacrifice values it lower, because Food and chip damage pull the deck away from a threat it needs to keep swinging.
The liability is that the trigger fires on attack, not on cast, and TMT's removal is built to punish exactly that window. Grounded for Life is cheaper against a tapped creature, and Stomped by the Foot can kill the pilot in response to the attack trigger before the counters resolve. Flying or other evasion is the out: it forces the removal onto the counters instead of an easy chump. Maindeck wherever you have a one-power on-type body, which is most green and black decks.

