Great stuff, been looking for something like that for ages. However it took me some time to figure out why it does not chroot on one of machines, for an account with non-default home dir ( not /home/$user ),

It does not read the home dir from /etc/passwd, but from /etc/ssh/sftp_config 

I was getting access denied error for the home dir specified in /etc/passwd ( not /home/$user ) when issuing ls command, and pwd returned the complete dir not just "/"

 Sorted that by adding

<Group mygroup>
        Home                    /smysftpfolder/myuser
</Group>

to /etc/ssh/sftp_config