Thank you Barnuble,
"Save Beside" works great. Had seen it before, but didn't connect it to portable mode, the name suggested some kind of sidebar layout to save or not to save. Anyway, it's truly portable now.
Talking portable: It were nice if users could specify their own external players (set up via portable/ relative paths to the app folder) - to be independent from the host systems and their crappy players. Say by entering a line in the ini-file that specifies what player to use: ..\..\SMplayer\SMplayer.exe
or ..\..\vlc\vlc-portable.exe
something like that.
Also found out about how to provide mplayer in the app folder, to avoid unpacking it each and every time. Shortens startup time.
The only showstopper that keeps me from using it, is the dreadful browsing procedure. It's one thing to use the breadcrumb bar of a file manager, or hit Return a bunch of times to dive down into the depths of subfolders. But then having to do it all over again in HMP is just too much. The font size and +-signs come out very tiny on large screens with high res and high DPI. And it's quite a long way to drill down the folder branches. Only to start all over again at the next go-around, all the way from the top level root.
I don't mind the browsing tree at startup. If only it would appear already drilled-down to the spot from where I started HMP, the path I provided via commandline. They way it works with other Compare-tools (WinMerge etc) or Sync/Backup tools - they all open with the paths provided by command line arguments. Which makes these tools integrate nicely with your main work environment.