The alien package installs the vcdiff binary for your convenience but this module uses the libvcdenc.so and libvcddec.so shared libraries so that the diffing computation is done in-process instead of forking processes.
Even with the streaming API open-vcdiff has a hard upper-limit of 2G file sizes and the default (which this module hasn't changed) is 64M so be warned.
If the source argument is a file handle, Vcdiff::OpenVcdiff will try to mmap(2) the entire file into memory with Sys::Mmap. As well as adding a dependency, this means that source files must be able to fit in your address space. Because of the file size limitation described above, this shouldn't be an issue. See the "STREAMING API" section of Vcdiff for more details.
The Alien::OpenVcdiff dependency takes a long time to compile compared to Vcdiff::Xdelta3 although it's not a completely fair comparison because the alien module also runs open-vcdiff's test-suite (which is good).
The library writes to standard error in the event of errors and I don't believe there is any way to silence these messages.