I bought the three volumes of this at a shop for a total of $6. I think I got my money’s worth.
I can’t say that Batmanga is good literature or deeply affecting, but it was better than expected and made for a fun couple of evenings. The art is consistently solid and it’s cool to see Batman and friends drawn in that old time style. Most surprising of all, the stories do not suffer from the bizarre leaps of logic that often appear in manga of this era. Yes, Batman does have a battle royale with aliens, but it generally all makes sense!
Unfortunately, few notable Batman villains appear and the original ones are almost all goofy. If you’re a giant Clayface fan (lol), you’ll be pleasantly surprised.
If you see this for less than $10 total, and have any attachment to Batman, I think you might get some enjoyment out of it. You won’t be missing much if you skip it though (except for Batman fighting aliens). Reading one volume or even one story is enough to determine whether it's worth it to continue.