Without the model number it is difficult to comment on your Juki serger prospect. Given the stitch speed of your Juki sewing machine purchase, you apparently bought an industrial - not a domestic - machine. If the seller is the same, you may be looking at an industrial serger. Things to consider: what are you sewing to need an industrial vs. domestic, condition (you say it runs), is an operator's manual included or available online (sergers are more complicated in their set-up and threading), are the needles available for purchase (some sergers take special needles vs. domestic sewing machine needles)? $300 is on the low side for an industrial serger. Industrial machines tend to be single function/purpose machines while more current domestic machines tend to be more multi-purpose. You can buy a very serviceable, 2/3/4 thread domestic serger - a brand new Brother 1034D - for $175 - $200 - do you need more than that? Go to Patternreview dot com and see if you can find a review on the model you are considering. There are lots of aspects that go into a purchase decision. Good luck!