Prism99

I bought a 4-thread Bernina serger about 15-20 years ago, around the same time I bought my Bernina 1230 sewing machine.

If I had gotten air threading with my serger, I'm sure I would have used it a *lot* more to make clothing for my daughter. The serger was not something I used every day, so threading was a recurrent problem for me (even with tying threads together). As I have gotten older, getting the loopers threaded correctly has become even more of a challenge -- because my eyesight is not as good as it was, I cannot bend and turn and twist as easily as I used to, and my fine motor control is not quite as good as it used to be. If I had it to do over again (hindsight is so wonderful!) I would have paid the extra money to get a 5-thread machine with air threading.

5-thread means you can set the serger up to do a cover stitch (if you check the hem of a t-shirt, that is a cover stitch; two parallel lines on the front, a cut edge that is overcast with a zigzag on the back). This stitch helps make your garments look professionally finished, plus it speeds up garment construction -- especially if you plan on making lots of children's clothes.

Air threading is expensive but, in my opinion, it makes a serger much more user-friendly over the long-term. Things have changed over the years, but I believe Babylock has a good track record with air-threading sergers. I would never buy the all-singing-all-dancing sergers that are on the market today. They must be great for creative people; however, I know all those options would simply confuse me.

If buying used, you want to make sure that the serger has differential feed. Differential feed is extremely helpful when sewing on stretchy fabrics, and there are old sergers out there that do not have differential feed.

Edit: For me, setting and re-setting thread tensions was not an issue so I would not see automatic tensions as being something I would pay for. But I would pay for air threading!