I considered a manual sharpener. But it needs its own heated room, it's messy, it's very heavy so cannot easily be moved about, and it takes time to learn. I have one pair of skates to sharpen, and no-one to teach me, or spot the mistakes I make and reinforce. So a machine makes sense. As to them being made of lots of plastic, there is a rec team in the UK who own both Sparx and Prosharp machines, and they take them all over the UK and even overseas, and they say they are both robust.