With this little aquarium vacuum cleaner costing only about 25% of what some others do I was not expecting perfection. I am however very pleased with it as it made short work of cleaning up after our large pleco (who is a seriously messy fish!). It primes readily so long as you have the bag holder pointing sideways rather than downwards (which otherwise can cause the pump to air-lock). It has just about the perfect amount of 'suck' and you can hoover around the plants without sucking them out of the gravel. Its reasonably quiet so should not cause your fish major palpitations.
It all comes apart readily for easy cleaning.
It has only one slight fault which is easily to get around. The switch is hard to operate when the battery compartment cover is fully screwed home. I found it was much simpler to just set the switch to the on position and turn the thing on and off with a half turn twist of the battery compartment cover. They could actually have made it even cheaper if they had missed out the switch and relied on this method of turning it on and off!