There are various options depending whether you want mains, battery or petrol, and of course your budget.
I used to have a relatively cheap MacAllister (B&Qs own brand) 18V strimmer that took plastic blades instead of nylon line. They do save the frustration of snapped line all the time however I did find they wear down relatively quickly so need replacing frequently.
I now own a Stihl 18V strimmer which can take spools of nylon line as normal, or a "PolyCut mowing head" which takes plastic blades similar to the MacAllister. I think most of the Stihl range can take both but obviously check before you buy.
I also own a Stihl petrol brushcutter which takes nylon line (much thicker nylon line than the cordless) but can also be retro-fitted with a metal cutting blade. I've never used a metal blade with it as I've found the thicker line is strong enough for what I use it for, and the metal cutting blades can be rather viscous / dangerous so probably not appropriate in many situations. I would certainly want to wear long trousers and sleeves and a full face mask!