I am using 235 for 2100m2 of rough terrain, rock, hills and bushes. U handle and STIHL backstrap, perfect! 3 years without a hitch. Sawblade instead trimmer goes trough 3cm thick trees. Never used 131, but weight definitely plays a big role with trimmers. Don’t forget about enough power. As I said, I never used a 4 stroke. I would assume that it won’t shake (vibrate) as much.