After getting through the setup, the usage of the SIM was very smooth; speeds were around 3G, which is more than enough for Google Maps and loading standard websites, and coverage via Docomo was great, even outside Tokyo

Good coverage in the cities I visited in Japan

Tokyo is great and all, but I actually spend more time in Japan's smaller towns/cities and rural areas and I have found that NTT has great LTE coverage even in lesser populated areas as well

The coverage was excellent in all of the many major cities and even underground.

Subways systems had great cell coverage underground

Easy to install and excellent coverage.

I prefer other SIM cards which just throttle you down to a slower 4G speed.