I like the Watson style loader the best. Usually I load cartridges which already have been used, with the film cut off close to the felt. But fresh ones, for which you still have to attach the film to the core, will work as well.
Just open the loaders lid with the gate closed. The film should stick out of the gate by 1cm. If necessary cut it, but that should only need be necessary the first time. With the lights on use two short strips of tape to join (on on each film side) the two film ends. Its easy to do, I'm sure anyone can figure out their own technique.
Switch off the light, open the gate and pull up the cartidge to place it into the winder part. With your finger tips check that the film perforation is running over the counter gears, close the lid and turn the gate all the way open so that the lid is locked by that little tab.
Lights come on, you can set the counter to the start position, spool as many frames as you like and close the gate. With the lights still on you open the lid and cut the film one cm (or as short as you can handle) from the gate. The exposed piece of film is just the right length for the leader. Cut it into shape and it's done. With a normal SLR you should have no or minimal fogging at the film end.
My other loader, which is similar to that Kaiser one, has a light trap without felt under the lid. So some light will penetrate a short partial length of the trap. I just don't know how much film is fogged. For that reason I cannot attach the next cartridge with the lights on, and that makes it more troublesome to use. Also, when finished spooling, I need to open the lid and cut the film in the dark to make sure, again, the the next film end isn't fogged.
That being said, with the Watson clone I made the grave mistake of opening the gate and lid at the same time. Yes there is the locking mechanism, but playing around to establish my method I did a kind of override. So I fogged my fresh bulk roll of HP5+. I'm still finishing the last feet of it in the loader, now.
The result was quite interesting. I had to dispose quite a few windings of film. Because the gate was a shaded, due to the angle of the light source, the fogging largely stopped except for the side of the film, where it made it through most of the roll. That means I have usually two frames per film roll that are partially fogged at the bottom of the frames, about one frame width. That's a thorough, and for now, ongoing lesson. But it didn't stop me from enjoying the results. I switched from Tri-X so I can bulk load, because it is a a great experience. OK a bit much excitement this time round. It also make it so cheap that I just don't think about the cost of HP5. I simply use it. Ok, not as trigger happy as with digital but it feels just as carefree. Also I can have different lengths of film in the cartridges.