yeah, i was wondering the same some days ago. it's too cheap to be really true, but convince me that i'm wrong.
realm crafter 1 games look mostly awful, fut that can be caused by the bad artists as the target audience is for even more beginners than 3dgs. i'm waiting for realm crafter 2 (rebranded "professional"), which offers shader support etc.
in general dark/blitz basic games and their engines did not overwhelm me referring to rendering speed (>fps creator), i wonder what it looks like with hunderds of players.

there is a free alternative which i didn't try out, too: multiverse.