how many calories are in a house gecko?
 

Simply put, I saw house geckos for sale on multiple feeder websites, so I wondered if they would be better or worse than mice for a small snake.

The calories are irrelevant. If you have a snake that eats rodents, feed it rodents. If your snake will only eat lizards, then you are forced to feed it lizards.

The pathogen transmission potential from feeder reptiles outweighs anything else. Cost is the next downside to feeder geckos, and irregular availability (i.e. when geckos aren't available for months your snake starves) is downside number three. There are more downsides, but those are sufficient.

My snakes would only eat geckos when they were small, and they did fine on them for years (it's a slow-growing species), but when I was able to switch over to chicks they started to grow much faster.

So, in my experience they can survive just fine on geckos, but they obviously benefit from larger prey.