Let me start by saying these feeding rings come in a handy set of two - one round and one square. The square one (10x10cm) feels more substantial in my 40-gallon tank, while the round one (7.5cm diameter) works better in my smaller quarantine tank.
The suction cups are surprisingly strong - they've stayed put for weeks without needing readjustment, even with my rowdy goldfish bumping into them. I particularly like how the adjustable joint moves with water level changes during cleaning days.
Here's where it gets interesting: while they do contain most floating food, some pellets inevitably escape underneath or over the edges. It's not perfect containment, but definitely better than free-floating chaos. I've found they work best with larger floating pellets rather than fine flakes.
Unexpected bonus - they're fantastic for corralling floating plants! My water lettuce used to clog the filter until I started using these rings as plant corrals. This unadvertised feature alone makes them worth keeping.
Would I recommend them? If you're looking for complete food containment, these might disappoint. But as multi-purpose aquarium tools that mostly keep food in place while serving other functions? Definitely worth trying at this price point.