I often print less than healthy materials like ABS, and I rarely use the basic spool holder.

Usually I print straight out of a drybox or a filament dryer, so that little hole is one of the many places where unwanted particles and smells can escape from.

I wanted the plug to take up as little room as possible while still being easy to install/remove.
In this case you can still do so by hand if you've got a strong grip, but I've added a slot on the back so that you can use a flat-head screwdriver to help you.

I printed mine in ASA on the standard profile on my Centauri Carbon with normal supports (no special settings) and was able to easily remove the supports with a pair of pliers.