I recommend the metal string and handles for DIY, its cheap and usually fast (depends on your talent for it) If the windscreen was previously replaced its usually a bit harder to do, because people use too much glue.
3/4 - 1 metre wire works best (depends on space inside car). Don't try to pull too hard, you want to get the wire hot through movement. sign for doin it right is when it starts to smoke a bit. guide the wire around the screen so you dont cut your paint, apply tape where it is a bit tight an on corners, same for dash and roof lining, can even tape some cardboard stripes close to the screen if you want to make a 100% sure.
cheers, bene