Thanks for the help guys

Yes this file is old, but it still works for mounting ADF and ISO images so that they can be accessed like any other device on the Amiga. As for HDF images, megacz mentions the following in his readme file:
"WARNING!
I do not recommend to use filedisk.device for hardfile mounting,
as it is able to write only the very first 16 megabytes and may
corrupt ur hardfile!!!"
I decided to try this anyway, so I made a 32MB hardfile in WinUAE which I copied to my A1200. After mounting the image, I started copying some files to it and expected a lot of problems after reaching the 16 MB barrier, but to my surprise it went fine. Then I tested the virtual drive with DiskSalv2, where it found no errors. Later I have tested filedisk.device with both 100 and 200 MB HDF files by using the same methods, but have not experienced any problems yet.
So it turns out that megacz was wrong. My guess is that either the HDF format has improved a lot since 2006, or he was using a wrong mountfile.
The nice thing about filedisk.device is that it works on any Amiga with Workbench 2.1 and up (the Mount command in WB2.0 doesn't like anything other than numbers to be specified as Unit). I am currently working on a requester based script which uses filedisk.device, this script will allow the user to mount ADF, ISO and HDF images with just a few mouseclicks. It is mainly meant for my Amiga911 project, but will also be uploaded to Aminet.
BTW. The reason why I started this thread, was to find out if there exists a workaround for the WB2.0 Mount command, but it seems like there isn't (other than using a later version of Mount).