I wouldn't be without mine. I bought it about 5 years ago, just a cheapy because I was unsure how much I would use it. It's great for neatening seam allowances on woven fabrics, as it tames fraying fabric beautifully. I love the finish it gives to a sleeve-head/armhole seam. On knits, it copes with everything. My sewing machine didn't like one particular synthetic Ponte fabric, but the overlocker just stitched away happily. It doesn't compare with an overlock stitch on the normal sewing machine, it's so much faster and it cuts off the excess.
One day I'll upgrade to a better model now I've found out how much I use it.