I’m not really the target of your question since I’ve really just used bookwalker (and I’d also be curious to hear from anybody who’s used multiple), but I do get the impression that the various ebook sites (and bookwalker is an ebook sales platform, larger than just manga) are largely similar and it’s just a matter of which you’re introduced to and develop a library on first.
Once you start buying books on one site, it’s easy to want to keep buying them there, after all… so comparison shopping for platforms is harder.
Especially since I don’t think there’s going to be too much difference in actual available content. In my experience, not finding something on Bookwalker is pretty rare in the first place, and when something’s not on my impression is it’s because there’s no ebook edition at all (like as far as I know, there’s no other site hoarding Yotsuba&! ebook exclusivity for example). (It’s possible I’m overlooking some categories without realizing it though)
The main reason I ended up with Bookwalker is really just that people on this forum seem to tend to use it (like this thread exists) so I heard about it, and also that I could sign up outside of Japan with no issues at all. My impression from hearing about amazon/kindle, for example, is that you would potentially have to go through some rigmarole to get it working properly with Japanese books outside of Japan (but I don’t know the exact details).
From a learner’s perspective, just knowing that other learners have used it and could be asked if you have problems can be a major benefit in and of itself, since I would be hesitant to try a tempting-looking site if I wasn’t sure it wasn’t region-locked in some unexpected way. And in my experience at least, there isn’t anything like that with Bookwalker except the occasional smattering of listings that are Japan-only for some reason (but those are few and far between).
Beyond things like that, I think it’s mostly going to be slight differences in rewards programs, selection, and app preferences.
I found this extensive article (in Japanese) comparing lots of sites, though:
The first one they listed, Booklive, is recommended for
- daily coupon gatcha
- easiest to use
- lots of stuff
- free things.
and recommend it especially to people new to ebook sites.
If you want to look into multiple before committing, seems like that would definitely be one to check out (that coupon gatcha sounds fun but kinda dangerous…). Although it seems like (one of?) the rewards, “T points” are some kind of general reward system that ties into other things, which might be a downside if you aren’t in Japan.
In contrast, they give Bookwalker a 4-star recommendation instead of 5, and recommend it for people who:
like light novels
want special bonuses with the books you like
Buy more than 5000 yen worth of books a month
That pretty much jibes with my experience. It makes sense that people on this forum would tend to use Bookwalker if it’s especially good for light novels, (also, I think it’s affiliated with Bookmeter, which is another site people in the extensive reading thread use for tracking books) and Bookwalker’s coinback ranking system seems a lot more generous in bulk than say, Booklive’s from what I can tell. I… have fallen prey to that in the months since I’ve found out about it… They’re good at incentivizing buying a lot of books.
But again I think it really just depends on slight preferences or circumstances on your part. And you’re right, it seems like there’s a lot of options! When points in one site’s favor over Bookwalker are stuff like “has a lot of books, coupons and free stuff; good for manga” it goes to show that they’re contrasting things based on what’s the Very Best at something, since in my experience Bookwalker also has tons of books, coupons and free stuff and is very good for manga. So I think if you just want 1 platform to enjoy buying and reading Japanese ebooks on you can surely be happy with any of these.
Hope all that helps a little at least!