The latest version fixes a few really stupid errors. RSN tm . It is very simple and should be easy to use. With it you can edit sectors, save sectors to a file, write a file to sectors, etc.
Commands are case sensitive.
Commands which write raw sectors will always ask for confirmation. All commands that write to the disk will always ask for confirmation. Look for unused sectors on HDDs and experiment there first before editing used sectors. Of course you can always mess around with floppies first. This way you can test all write commands to see what the BIOS call parameters will be.