I tried Ubigi and it may be adequate for light use but I was in Japan for about 3 days with a relatively big list of errands to run and felt it got in my way other services haven't when I've used them in the past.

Ping in and around Tokyo was upwards of 200ms. Speed can be pretty rough during peak times, probably due to being deprioritized.

Traffic is routed through Singapore, but I'd occasionally be GeoIP'd to France and see French ads. Some sites+apps would not work, possibly due to some of this weirdness.

I've also seen situations where it'd take 5-10 seconds for data to start working again when waking my phone from sleep. This got pretty annoying as I'd sometimes quickly want to check if the right train is in front of me on the platform. I haven't run into this with any other mobile data service in the past.