Hi,
I presently use all Bernina machines except for my little Singer Featherweight. I think their bobbins hold a lot more thread.
My Bernina Embroidery Machine the 650 Deco has a drop in bobbin. I find if I buy the prewound bobbins for it they seem to last forever. There is nothing more irritating than running out of bobbin thread in the middle of an embroidery design. As for adjusting the bobbin tension. I purchased a second bobbincase to use with heavier threads so that I can play with the tension. While I know how to do it I have never actually used that method. You can handwind the bobbin with really heavy threads, decorative or otherwise as well as even ribbon. If you sew on the reverse side of your project the fancy thread or ribbon shows up on the front when it is finished.