If one wants to put these old machines to good use, it's worth remembering (after checking that they still work), that these older machines (the iMac and the MacBook) are still user-upgradable.
The iMac should allow for 4GB of RAM (of which only 3 will be usable), the MacBook unofficially supports 8GB. Add in a cheap S-ATA SSD, and for some not too high, two digit amount of EUR or USD, these machines will be actually useful for someone.
Virtually every step in the iFixit upgrade guide for separating the screen glued onto my iMac was followed by "if you do this wrong you'll crack the screen" so I've stuck with it as a beautiful screen for connecting to other more powerful machines.
I was going to add an caveat about that, but it turns out, that for the iMac 5,1 (the model discussed in the article) RAM upgrades are easy [1] (SSD not so much, but it should still be better than some of its aluminum successors [2]).
That said, I definitely agree and advise:
Before you order parts to upgrade things, check whether you feel up for the install procedure.
I upgraded both of my parents iMacs (about 10 years old now, but importantly with USB 3), which would otherwise have required screen removal to do the drive, by just hooking up a portable USB SSD, making it the boot drive, and taping it to the back of the machine. Huge improvement over the HDD.
These older iMacs like the one in the article didn't use glue yet! That only started with the 2012 ones iirc. So anything before that is pretty easy to fix or Upgrade!
(Especially the old aluminum ones, they just had magnets holding the front bezel in place)
I upgraded the hdd to an ssd in a 2009 iMac.
Don't think I ever noticed the "you may crack it" warning.
Honestly it's not too bad.
The more painful thing is actually working on the guts while also trying to hold the screen up (because it's attached to things).
That said, the RAM is user-accessible on these older iMacs from a tray at the bottom edge of the screen.
The iMac should allow for 4GB of RAM (of which only 3 will be usable), the MacBook unofficially supports 8GB. Add in a cheap S-ATA SSD, and for some not too high, two digit amount of EUR or USD, these machines will be actually useful for someone.