File size in different devices
Yes. If the files are identical, by definition, they should also be identical in size, regardless of platform (Unless the file is a sparse file, and/or the mechanism by which the FS driver of the platform reports file sizes is buggy).

But for identical apps, however:

Not necessarily. The file size mostly differs for native-compiled executable code (ARM vs. x86 chipsets,etc.), graphics resources supplied as per the device's graphics capability (OpenGL ES 2.0 vs 3.0), and so on.

In your case, it would be better to compute and compare checksums for the files, instead of size, as they depend on the contents of the file which should not vary from platform to platform, except as stated above.