Several of the ladies at the senior center have opted to get the lighter machines to take to class. These machines all have plastic gears and even though they sew nicely at first, it seems that over time their stitches don't stay really true. One example I can think of at the top of my head, is that the straight stitch started stitching at an angle. If you think of a model (woman) who walks heel to toe and liken this to a normal straight stitch, then think of an ordinary woman (non-model) who walks with uneven steps, this would be how the stitches would look on the smaller, cheaper machines. I don't know quite how to explain it any better. It did not seem to bother most of the owners, but it would drive me crazy. The other thing I noticed was that the tension seemed to go screwy more often than on a regular machine.
Please understand, I am not knocking all of the smaller machines, I am just drawing attention to the things that I have noticed and the complaints that I have heard and am suggesting that you check the reviews carefully.
If you are lucky enough to find a featherweight, it is still my go to machine to sew on and it is lighter than most machines, dependable and they rarely have any high-cost repair bills.