I'm likewise a fan. It's significantly unique enough that my fridge always contains a jar of Hellman's and a bottle of Kewpie... and frequently a little tub of homemade. I... uh... like mayo.
I tend to mostly use it in tuna and egg salad, probably because Japanese tuna and egg salad is fricking awesome and using Kewpie is the only way I've been able to get close to it. It's also a really good foil for sweet soy-based sauces, hence the use with okonomiyaki. I also wouldn't want any other kind of mayo on takoyaki. Not that I make takoyaki.
In any case, the difference is significant and definitely merits a try, even if it doesn't end up working its way into your regular condiment rotation.
Dominic Armato
Dining Critic
The Arizona Republic and
azcentral.com