I bought some electronics from dx.com few times (China) and that Banana Pi website is typical Chinese case - you can get the product from one of their international stores but don't expect cool documentation, tutorials and whatnot. It's up to the community outside China to make it live (like pcDuino).
As for performance comparison that may differ a lot. The CPU is faster, the RAM is faster and it's 1 GB, you have SATA so in general I/O operations should be very fast. I've tested few A10 (older, single core) boards (pcDuino, Cubieboard v1) in the past and in some phoronix benchmarks like phpbench or pybench Pi was 2-or-more times slower, but at other like dcraw - quite close. Mali400MP2 is dual core GPU unit. It's hard to compare it to VC4. It can run Android and Android apps and most of the non-demanding games. Raspberry Pi SoC is to old for Android. On classical X.org Linux Mali400 isn't cool and it's hard to get 3D acceleration etc. Like the Cubieboard v1 was quite nice on Android but classical Linux desktop wasn't much better than Pi in terms of responsiveness. Even quad or octa-core Samsung Exynos board may have super high performance and PC-alike desktop behaviour but if you go into graphics - Mali will fail. Drivers were written for Android, and more Linux GPU-demanding apps were written on x86 with Intel/AMD/nVidia graphics and X.org APIs (that's why things like minnowboard max will quite likely allow you to play OpenArena, Xonotic, UrbanTerror, Nexuiz etc.). Wayland may change something as it can use Android drivers, but those games and alike apps must take advantage of the new APIs (full screen apps like games don't actually use the display server AFAIK).
If I would want a Python scriptable board with GPIO stronger than Pi I would probably took PcDuino v2 (also A20). HummingBoard is interesting as it's going into quad core, no Mali but also "Android GPU" may hit it. It all depend what you want to do with them. It may be hard to make them a typical low power desktop PC, at bit more demanding server (database, dynamic website) load they will fail on RAM and partially computing power (or also I/O). They are best as media players, some as Android media "centres", but most of the fun is with hacking - hardware and electronics. For that you need docs, libraries and someone to port third party libraries if needed