Well as for fuel additives I'm not a big fan of any of them. But as for gelling issue you need something for those really cold days. But there is a few problems.
1. Most all anti-gel products start out with xylene as a base.
2. With any cetane booster and anti-gel produces you going to loose both lubricity of the fuel and also BTU content and get reduced MPG's.
So with that being said I would consider carry a bottle a PowerService 911 but I would not use a product in every tank. I'd only add it if the fuel was actually gelling up and fuel pressure is falling way off. It normal to see lower fuel pressures during the winter time but big falls in pressure is telling you your filter is plugging with clouded fuel.
Now here is a theory I've been playing with but I've got no actual proof or testing done. When I've been using is snowmobile 2 cycle oil in the dead of winter. Out here in Idaho most all snowmobile 2 cycle oil has a pour point to -50*F. So if you adding -50*F pour point 2 cycle oil to -20*F pour point diesel fuel the 2cycle oil should reduce the pour point of the diesel fuel even lower. How much I'm not sure. Kind of like saying water(diesel fuel) freezes at 32*F but with a bit of saltwater (2 cycle oil) added to the water (diesel fuel) the freeze point should be reduced. How much it all depends on the mixture of the saltwater (2 cycle oil).