This is an important question. I'm actually seriously considering buying one myself, not initially for Nepenthes, but for Passifloras. My question is whether the cheap versions work as well as the expensive versions of a few years ago. If so, which of the cheap versions are effective and worth buying? My guess is that like anything else, they vary in quality.
Here's the Passiflora story, which I find most relevant. A few years ago, someone I know used an aeroponics machine at a university to root Passiflora parritae, a notoriously difficult species (and hard to find, etc.), as well as a couple of other species, including Lapageria rosea. He had spectacular results, especially with P. parritae, even after a couple weeks. The result was never publicized (which is why I'm not mentioning names). It wasn't sufficiently followed up on either. I think I'm giving a workshop on propagation at the PSI (Passiflora Society International) meeting on propagation, so it probably makes sense that I do it myself, rather than complain that it hasn't been done...
I'll post on a plant propagation group on Facebook (Tammy Romero's "Passion for Plant Propagation"
https://www.facebook.com/groups/1449885718568242/) and see if anyone has any recommendations for particularly effective cheap models. Perhaps someone has tested them rigorously, or perhaps there's word of mouth. I'm particularly interested in those that really seem to do well with the difficult projects. I think the simpler cases, such as cuttings that also root in water, are less informative.
I think it's likely that the machines that are most effective for difficult species of a variety of genera will also be most effective for rooting Nepenthes.