I have only used the electric models. The only downside is the requirement for a generator. There is a 21cc petrol-engined single-sided Little Wonder but as yet I have no experience of that model. Of course, with an engine it will weigh more.
Another trimmer that I would consider is the HS 82 T from Stihl. This is also a professional tool and has a high blade speed for a fine cut. Tanaka trimmers from FGM Claymore also impress me.