Geckos are very strong. They have slightly better tracking than Berserker IIs (the best tracking heavy drones) along with the same velocity, they have double the damage of Ogre IIs at max skill (the highest DPS heavy drone). And they are about 4 times as durable as typical heavy drones. Oh, and they deal all 4 types of damage.
There are situations where using T2 heavy drones is technically better, DPS-wise, specifically for shooting resist holes, but not by much. You can easily argue that the Geckos still win just through shear Tracking, being able to hit stuff like frigates with ease, especially on a tracking-bonused hull.
The single biggest argument against Geckos is their pricetag.