Pretty good output for the price, I agree!
There’s not really a right or wrong way with those switches, but I can explain the benefits to with and without.
With the veg portion on and the bloom off your light will have less output and cover less area. However your plant will have less tendency to want to stretch out under just the blue. Typically creating that tight bushy node spacing a lot of growers like to see.
When you add the red section, or bloom as I believe the switch is labeled, the plants will react by wanting to stretch out to that red spectrum. Similar to what plants do under conditions that don’t have enough light, but not as bad.
If you’ve seen plants that are almost as round as they are tall, and have very thick canopies, those were most likely veged under a heavy blue or cold white spectrum. If you’ve seen plants that are taller with large gaps between nodes and/or buds, those most likely had a lot of red in their veg spectrum.
Your particular light doesn’t seem to produce a lot of red according to the manufacturer. See pic below
Assuming that’s with both switches on, it doesn’t reach the peak of the McCree curve. So this wouldn’t produce as much stretch under bloom as a light that does. But I’m sure it would stretch at least be a little more than without. So to answer your question, go with just blue for a shorter more bushy plant, or both for a little bit taller plant in veg. And run that puppy wide open when you hit the flower stage. The blue isn’t as critical then, but the extra photons will help with yeild.