It’s basically deep-fried custard. Here’s a pretty good pictorial essay on it.
As to your other questions - what’s so good about Kao Leng Mian - it’s not so much that it’s good or all that great, it’s just the rarity of it which makes it noteworthy this side of the Pacific Ocean.
I mean, seriously, unicorns aren’t all that tasty. But if I saw one on a menu, I’d let y’all know about it for sure.
#CommiesHaveTakenOver