Honestly, you might have just gotten a bad unit or used it wrong. Those gadgets can work fine for basic home use if you follow the instructions to the letter. It's not meant for a chef's knife, just keeping a decent edge on your everyday stuff. For eighty bucks you were paying for the convenience, not a pro result. Sometimes the problem is expecting too much from a simple tool.
The real issue is how they sell these things. Marketing makes them look like magic, so people get mad when they're just okay tools. That gap between the ad and reality is what kills the vibe.