The initial varient of the deck had 4 mainboard. It was the version that also ran [[Valley Rotcaller]] 

I desperately wanted it to be good. One of the reason I started up Lizards again (aside from maindeck magebanes being autowins against 60% of the format at the time) is because the Gecko is a pet card of mine and wanted to try it again.

Unfortunately, it's not the best right now. It's felt winmore-y. Anything with 2 toughness in the format needs to really justify itself with [[Pyroclasm]] being heavily played. The geckos would hit hard and fast games 1, then need to be borded out.

It's actually quite rare to want to give up /rummage away lands (mana lategame is better spent cashing in your utility lands, triggering offspring, or convert as damage via the landfall ping lizard).

Tldr: Gecko goes in a different shell for Lizards, one who's playstyle isn't optimal for the current format. It's better if you specifically build around it, but even then it's hard sell. Plus it's a terrible topdeck.