Twin needles are easy, though you may have to play with tension on your sewing machine. Did you ever see the article in Threads magazine that Carol Ahles did about various twin needle effects? There's a nice summary chart, too.
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Remember, though, that coverstitching stretches, while twin needle stitching will pop.
Good idea.
I'm also firmly in the camp of "separate coverstitch machine". Much easier. Current favorite among the standalones seems to be Janome.
Kay (with an ancient Juki-made Bernette 009D, fine for what I do)