I would first think through a few things:
--How much do I want to spend. The self threaders are nice but very pricey. If this were my first time using one, I would save my money and try the old thread it myself type.
--How much would I use it. [I use mine more for sewing or finishing seams on quilted items like purses or bowls or fleece blankets.]
I do have the Pfaff 4852 and love it. I can't justify the cost of the self threading serger.