The Freetel SIM didn't arrive in time for me to use it on my recent trip to Japan, I wish I could comment on whether it worked well.

However, since I was in China first, what I ended up doing was buying a SIM off Taobao and having it shipped to my hotel (arrived within 36 hours, sometimes can arrive as soon as next morning or same day).

Total cost? 54 RMB, or about $8. The card is for the Docomo network, 1.5GB LTE, unlimited data otherwise for 8 days. You have to download an APN profile and set that up before the card will work, but it was pretty painless even if you can't read Chinese. May need someone to help you select the card, but it works pretty well so far. Might even be able to get these sent to the U.S., or can always try the Freetel SIM for $12.99 on Amazon.com.