I’ve used both eBook Japan and Bookwalker (mobile mainly for both) and between the two I prefer Bookwalker for a few reasons:
- Easier to sign up for an account. eBookJapan recently became Yahoo!Japan and the signup process for a Y!J account is cumbersome–I think I recall having to input a JP address because I had to look up my Tenso one. Someone in the forum wrote a guide for it, but I don’t have the link. I think it was in one of the Absolute Beginner bookclubs.
- Has an app in the NA Google play store. When eBookJP merged with Y!JP the NA app is no longer available, and the new app is JP region only. You would need to either be in Japan, use a VPN, or other way to spoof the region. For me in NA, this was too bothersome.
- Bookwalker has both an english-translated-book site (global.bookwalker.jp) and the japanese site (bookwalker.jp). Your one account works for both, and both types of books will show in the NA app for reading, which is nice.
- If you highlight a word and hit translate it will pull up Google translate for whatever that’s worth. It’s also fairly configurable for font size and spacing.
- Price wise I think they’re generally about the same?
Right now there are a few books free to read you could test out if you wanted to.
I was using AmazonJP on my kindle until it started yelling about regions as well and liked it quite a bit.