In the possibly the best folding bike shop in Tokyo, Loro Slow, Bromptons pretty much rule. Another important store, Y's Road Ueno, carries Dahons, Terns, Birdys and Bromptons. I.e. the preferences in Japan tend to be similar as elsewhere in the world. If you go to a lower end, of course you will find plenty of brands and models you never heard of and for a good reason.