Easy to print, easy to assemble, and easy to use.  Meant to help hold down your follower tab while you load BBs so that your thumb doesn't have to.  The guide tabs help keep your speedloader from slipping off.

Use the catch portion to grab onto the follower tab, then shove the follower down, which lets you push the BBs into the channel directly from the front.  See pictures for details.

Uses a standard speedloader widely available from your favorite shop or Amazon.

A .25 nozzle is recommended, but this should be printable with .4 as well.  PLA or PETG is fine.