A serger will almost certainly make your sewing go more quickly. I use one to finish seam allowances, and I finish them separately after pressing them open. It’s much faster than zigzagging with a sewing machine. Just remember that a serger can also trim as it finishes, so you’ll probably want to practice a bit before using it. I like to finish the seam allowances without trimming, which just means that you need to feed the fabric through the machine so the cut edge doesn’t get trimmed by the knife.
It takes a little practice and patience to thread a serger, so take that into consideration when you’re deciding to buy. I leave either white or light grey thread in the machine so I’m not always changing it to match what I’m sewing, and I also have black thread on hand but don’t use it much because the re-threading is a bit tricky.
I would suggest that you avoid getting a combination serger-coverstitch machine and focus on getting a good serger with 3- and 4-thread options. While the coverstitch option is a nice idea, it’s very complicated and time-consuming to convert from serger to coverstitch. And the cost of the combined machine is much higher than just the serger.
If at some point you want to invest in a coverstitch machine, it’s much more convenient to purchase a separate machine than to have the combined machine, and it costs almost the same amount to purchase the two machines separately than to have the one combined machine.
