One by one
Batch Duplication – Commercial
We've not tried it but the "Vinpower Digital SD Shark Standalone Target SD/MicroSD Memory Card Duplicator" looks as though it might be a more reasonably priced solution (still pretty expensive though). It's stocked by quite a few retailers including amazon. We asked if it would work for SD cards used with the Raspberry Pi and got this response:
As long as the cards are formatted with HFS+, HSFX, FAT, exFat, NTFS, ext2/3/4 the duplicator should have no problem copying the data from the master to the target.
In regards to the size issue you are concerned about. There is a setting in our Duplicator called “Size Tolerance” that you may modify by percentages (e.g. 1%, 2%, 5%, Ignore, OFF ). This will allow you to use SD cards that are not consistent in the exact size. The user manual will have more information regarding this.
Raspbian uses ext4 so….
Then we asked again about the bitwise copy and got this response:
Only the SMART copy will care about the file system. Our RAW copy method will copy bit by bit without caring what file system is on it.
One of our clients has purchased this and seems to be having success with it. Please comment below if you've found any other solutions
Batch Duplication – Open Source
Looks abandoned and they didn't release the image file they initially hoped to, but maybe it works fine?