I just popped them into the bobbin case of my Voyager and they worked great! My bobbin case does not have a spring in the bottom of it. If yours does, I'm pretty sure you need to remove the spring in order for the magnetic bobbins to work.
I used this video to adjust tension:
http://www.youtube.com/watch?v=Q1mRhcquZTM
The above works for all machines, not just longarms.
I wouldn't adjust tension until you try it first. You might not need to change tension at all, depending on what type of thread you have been using. Or, you might need only to adjust the top tension.