A nice recipe and practically the same as the one I use, although I prefer to mix the cut-up rhubarb with the flour-sugar mixture and let it stand in a bowl, stirring now and then, while I made the crust.
Here are two tips (I've been making pies for over 40 years and they tell me I'm good at it): as a thickener for pies, flour can be unreliable, and I've had several failures using flour as a thickener in rhubarb pie (also in blueberry pie) although in apple pie it always works fine. So for the past 20 years or so I've used Minute Tapioca instead of flour as a thickener in rhubarb, cherry and blueberry pies, and the results are always perfect. No more rhubarb soup! Use half as much tapioca as you would use flour (in this recipe, 3 tablespoons of tapioca instead of the 6 tablespoons of flour.) Another tip: if you feel your rhubarb is not pink enough for an attractive filling, color the sugar pink before using it. Just put a few drops of red food coloring in a bowl, add the sugar and use a whisk to blend, or else put the color and sugar into a container with a tight-fitting lid that you can shake. If it doesn't blend thoroughly, don't worry--once the sugar and rhubarb are mixed and the sugar dissolves, the color will spread evenly in the filling.