I had the Lidl Singer and found it to be a disaster. Could never get a consistent tension and when I took it in for repair the result was still lacklustre. It was also so loud and rattled the whole table top in comparison to my Juki. I felt like the Singer just wouldn't last that long.
Sounds like it was faulty, or maybe a different model (perhaps not the S14-78). The machine has suction cups underneath and it moves a bit in operation, but the vibration is dampened by the suckers. Mine is no louder than a sewing machine, has free-arm capability and it is possible to disengage the knife.
For something that costs in the order of £160, I think it is excellent value, finishing edges has never been quicker or easier. Previously I had been using a zig-zag stitch with an over-edge presser foot mostly because the zigzag is much quicker than the fancy over-edge stitches. The overlocker is so much faster.
When I first got it, I had the problem of loops hanging over the edge but this was quickly fixed by adjusting the stitch finger lever one mm or so. Nowhere in the manual did it mention that!