I had a Timberline 850 and then upgraded to the new second generation Timberline 1300. The Pro's are the obvious increase in cooking surface. I really haven't found any cons. I never had a problem with either.
They share the same design, just size difference. I don't cook for more than 6-8 so the 850 was my choice for a more compact unit. The 1300 may use a touch more fuel but it has way more capacity.