A robot vacuum cleaner can be a handy helper around the house, but its usefulness depends on a number of factors.

Suction power is obviously very important. The stated wattage of a particular model isn't really useful in helping a customer assess suction power, so a practical test is recommended.

Claudia Oberascher, a household goods expert in Germany, advises testing out different models in a specialist shop before buying. Another thing to check is how loud the cleaner is when it's in operation.

Oberascher also recommends that you check the height of the device to see whether it will be able to fit under furniture such as sofas.

How exactly the device works and how it orientates itself in a room are also important. The more expensive models use a built-in camera and sensors to measure the room and avoid obstacles.

Low-cost models in particular often can't get over door thresholds and have to be lifted from room to room.

Some models let you set a start time or allow you to control them remotely using a smartphone app. After the work is done, the devices automatically return to their charging station.

As a rule, robot vacuum cleaners are less powerful than conventional vacuum cleaners, Oberascher says. The dust container is also much smaller.

For that reason they're best suited as a second vacuum cleaner to augment rather than replace a standard vacuum cleaner.

 - dpa