How about "Keep satisfying customers" Less information. "Keep" doesn't necessarily mean changing what you do. In other words, "keep" could mean "x, x, x,...",

How about "Keep satisfying customers" Less information. "Keep" doesn't necessarily mean changing what you do. In other words, "keep" could mean "x, x, x,...", while "iteratively" definitely means "x1, x2, x3,..." The greater precision is worth the awkwardness, and anyone who is unwilling to look up a word probably shouldn't be doing a startup.