The half round, (or two quarter rounds glued together), used for opening seams is called a Strip Stick. They are available on line. You can make your own easily. Pad or not, cover or not. A long one is 44 inches long, for WOF strips. And there is a shorter one.
I found an easy way to open seams is to press it one way and then press it the other way. That way both seam allowances have been pressed aside and open easier.
I don't press seams open unless it is the center of a star where many seams come together.
I was taught that stitch in the ditch was done as close to the seam as you can get without catching the fabric from the other piece. When finished correctly, you can't see it unless you pull the two pieces apart and look carefully.