Whilst replacing the grout in a large shower enclosure I tried four different tools. This electrical tool was not the worst, but neither was it the best. It was extremely slow in removing grout and, unless carefully controlled, could easily wander off course and scratch the tile surface. Also, as others have commented, you cannot use the tool for long due to the vibration. The really useless tool was from PlasPlugsPlasplug Gr215 Grout Remover
, its steel blade was too thin and wore out the fastest. A grout remover from Homebase with a tungsten carbide tip worked quite well. But the star performer was the Vitrex Heavy Duty Grout Rake Vitrex Heavy Duty Grout Rake Remover + 2 Spare Blades
. This tool was the easiest to use and removed grout very efficiently. I was able to complete the task in a couple of hours after wasting longer than that trying to use the other tools.