Right, but balanced and unbalanced Feistel networks let you turn the 16-byte AES block into an arbitrarily small PRF.

Well, yes. But at this point you're just making a new cipher with AES as the round function. And I think it should be at least as safe as the round function?

I have not checked lately, but is it actually the recommendation for format-preserving encryption?

	▲	tptacek an hour ago \| parent [-]
		I don't know about "the" recommendation, but it's how NIST standardized it (FF1 and FF3, both Feistel networks) and in the NIST rubric these aren't "new ciphers"; they're "block cipher modes". I'll say I'm more comfortable using a straightforward FPE block cipher mode with AES than I am repurposing a weaker lightweight cipher to take advantage of its 32-bit block size.