I have an old White serger that has served me very well. Yes, at first threading is difficult, but with practice, it gets better. The lower looper is the hardest for me because of the delicate threading tool used to get the thread through the part below the needles. My old machine (1987) has markers for each thread passage. All I have to do is follow the path of red triangles, circles, diamonds, and squares.
Someone mentioned getting a good stitch after threading. If I don't get a good stitch after I've threaded the serger, I cut the threads and start over. I find I save time by doing this.
Also if I need to adjust the tension knobs, I turn all of them back to zero and work my way back up again.