They are useless. I've had electric, petrol, and now battery with blades not line. The electric one (Bosch) was strong enough power wise but the cord kept breaking frequently and the so called bump feed mechanism never worked from day one. The petrol was better (brush cutter that could swap the head to cord strimmer) but again the cord snapped frequently and it was a bitch to start. Finished up using cable ties instead of the cord but hey still broke, but at least it was easy to put two new ones in. Recently purchased a battery powered one with replaceable blades similar to a Flymo. A couple of seconds to change blades, and blade wear is as expected, but the unit struggles to cope with anything longer than a few inches. All in all, the most useless foccin machines ever invented.