Easy to use module, just stumbled a bit on the right option to pass to the constructor for use with ssh -s sftp:
more => [ -o => 'StrictHostKeyChecking=no' ]
Might seem obvious but since Expect hides things a bit, I could not see it at first (IIRC).
The module is great, interface is simple to use, more (much more) reliable than any other SSH/SFTP module I tried, and the developer is wonderfully kind and reactive.
My use for this distribution is pretty basic: I needed to have a program connect to an sftp server and upload tens of megabytes of data automatically, BUT no ssh was available so we had to go through a squid proxy allowing us to CONNECT to the other side on port 22. Implementing an on-demand connection with Net::Proxy took a fork() and 5 minutes (2,5 reading the doc, and 2,5 writing the code). It's stable, faster than the uplink would allow, easy to use, etc. Great stuff.