GT is being kind, I have helped with some of the early work and testing and have 4 of these drums myself. I needed them to fill up my P Kasten that holds 5 mags and the loader! Picture below shows an original Bing type 2 on the left and four of the Numrich/GT repros.
Some do work better than others, and it is a little tough to understand- but any given drum may work better in one luger than another!
The initial "problems" with Numrich's drums, though they are a close copy, was final quality control and a several faults when copying the original.
They were rougher inside, not always in alignment, the mainspring weak, the follower too long and flimsy, the mag tube too large to fit many pistols, and the mag catch slot in the wrong place!
All of these must be "right" and in sync with your luger for the drum, or for an 8 round mag, to function correctly.
The GT reworked drum you receive may work perfectly in your luger when received, or it may be need a tweek; or it may be the pistol that needs attention.
I've said before, the pistol must run 100% with 8 round mags and your ammo. If not, don't even start with the drum. Get the pistol up to snuff first.
Then be sure the drum fits the mag well, it may need a little filing and/or polishing to slide in easily, as many lugers have smaller than average mag wells- especially earlier models and the occasional Mauser.
Don't be afraid to take the drum apart, following the instructions. You will need to re-lube the inside from time to time. I use Dupont teflon suspension lube, it is in a blue bottle with a red top.
This is the best one I have found, you can experiment with what you have though. I believe the Germans used "grease" back in WWI.; that would work too, but sure is messy. Most any oil will do, but won't last long and will need re-applying. Don't leave the magazine loaded or the spring under compression with the lever for more than loading and taking to the range(a few days).
When the drum is loaded, and the spring released; a light tap is needed to "settle" the ammo column in place. This can be done on a soft surface, your hand, or a tap with a rubber hammer. The more the drum is used the easier it becomes to load and use.
As GT said, starting with fewer than 32 rounds and working up is smart and will help you get a feel for the process. I start with 12 or 15 and work up. You don't have to shoot them out, just use a flat dowel to push the ammo out (into a box, or it will hide from you) and reload again.
I'm making this sound harder than it really is, but the result is sure worth it. Nothing like "dumping" 32 rounds from a luger with a trommel mag!
