installs freemind on Debian stretch(testing) - almost works, some issues, have asked in freemind sourceforge forum - https://sourceforge.net/p/freemind/discussion/22102/thread/8ee5e81f/

freemind-install.sh

# distro can be one of experimental, unstable, testing or ubuntu. 
DISTRO=testing

echo
echo install freemind
echo script by Andreas Krueger 2017, version v01
echo
echo must be run as root:

echo
echo adding repo to /etc/apt/sources.list.d/freemind.list

cat <<EOF >> freemind.list
deb http://eric.lavar.de/comp/linux/debian/ $DISTRO/
deb-src http://eric.lavar.de/comp/linux/debian/ $DISTRO/
EOF

sudo mv freemind.list /etc/apt/sources.list.d/


echo adding PGP key:

wget -O - http://eric.lavar.de/comp/linux/debian/deb_zorglub_s_bawue_de.pubkey | sudo apt-key add -

echo
echo updating:
sudo apt-get update


echo installing:
sudo apt-get install libbatik-java libjcalendar-java freemind
sudo apt-get install freemind-plugins-svg/experimental freemind-plugins-time/experimental freemind-plugins-help/experimental libjgoodies-forms-java/testing


echo
echo done.
echo if there were no errors, then freemind got installed. Type \'freemind\' to try. You might want to add a menu entry pointing to this file:
which freemind
echo

sudo apt-get update

still results in

...
Hit:18 https://netcologne.dl.sourceforge.net/project/ubuntuzilla/mozilla/apt all InRelease                                         
Ign:16 http://eric.lavar.de/comp/linux/debian experimental/ Release.gpg
Fetched 198 B in 0s (248 B/s)   
Reading package lists... Done
W: GPG error: http://eric.lavar.de/comp/linux/debian experimental/ Release: The following signatures were invalid: 98FB95CD6C404DF7E758601D27CD3F36869D2871
W: The repository 'http://eric.lavar.de/comp/linux/debian experimental/ Release' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

I have tried out your "please add some mechanism to check ..." script. I get this:

Warning: apt-key output should not be parsed (stdout is not a terminal)
ERROR: could not add repository
       comparison of keys's fingerprints failed
Warning: apt-key output should not be parsed (stdout is not a terminal)
installed: 
expected:  98FB 95CD 6C40 4DF7 E758 601D 27CD 3F36 869D 2871

I have also tried with

cat /etc/apt/sources.list.d/freemind.list 
deb http://eric.lavar.de/comp/linux/debian/ stretch/
deb-src http://eric.lavar.de/comp/linux/debian/ stretch/

but

sudo apt update
...
Err:13 http://eric.lavar.de/comp/linux/debian stretch/ Release                                                                                                                           
  404  Not Found
...
Reading package lists... Done 
E: The repository 'http://eric.lavar.de/comp/linux/debian stretch/ Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

and my forum discussion questions of February & March were ignored

• https://sourceforge.net/p/freemind/discussion/22102/thread/8ee5e81f/
• https://sourceforge.net/p/freemind/discussion/320014/thread/4a7c1fb1/

I think there's something wrong with Eric Lavarde's key. expired or something maybe? or his repo isn't signed with it (anymore)?

The following signatures were invalid: 98FB95CD6C404DF7E758601D27CD3F36869D2871

sort of calls this out.

US$0.02++