Yes x3, not sure about the squeeze on approach (A4 concern mainly) as my gear is studio bound, but I guess it makes sense for transportation purposes.
I bought one with my octatrack together. Although I use it the most time at home. The main reason is to protect the slot of the fader from dust when not using it.
The cover is also very handy for transportation. Together it behaves like one solid box. So you have not to think about breaking your encoders in a bag for example.
I’d love to have one for my A4 but until now I couldn’t justify spending 50 € on a piece of hard plastic. So it’s a towel for me. 
The PL-1 is only a piece of plastic, but it’s really worth the money, when you consider that it:
- protects your instruments against dust and harm at home or
when you transport them - looks very good (you can see the panel through the lid)
- weights almost nothing
- has the perfect size
- feels much more sturdy than those vintage turntable plastic lids.
You can also stack your elektron machines on your desk 
I have two pl1: one for the octatrack, the other for the analog four. I wish i had something like the pl1 for my mixing desk, the access virus and so on.
No joke, i’d advise to not buy an elektron machine without a pl1!
I’m not arguing against its usefulness Maybe next Paycheck.
I guess it goes without saying I’m a big fan of the Decksaver style covers for my gear these days:
I just wish I could find something similar for my Pod HD. 
In the past I used custom cloth covers from Lecover.com, and while they worked pretty good, these are far more protective and easier to keep clean as well.