I also have a 2004 Odyssey. My thoughts:
I'd stick with OEM Honda antifreeze. This is a fluid that you'll likely only change once every 100k or so. If you look at the cost savings over time, it's hardly nothing. I like to look at it this way-- if my replacement water pump were to die in only 20k miles (even if it were just a fluke,) do I want the non-OEM (mixed) coolant variable hanging over my head? Nope, if I'd used OEM coolant, I'd be 100% sure my coolant choice wasn't a factor. Therefore, I'm more confident diagnosing future problem(s) if I had used the correct fluid and not mixed them. You'll never get all the old coolant out, so you are mixing them, even though they are compatible. Consistency is a good thing
That said, both the Zerex and Pentosin products are compatible and will work fine. Zerex can be had in blue dye (like the OEM coolant) but Pentosin and Valvoline are red in color, IIRC. Valvoline Asian / Zerex Asian are the same product other than perhaps the dye used. Again, unless I were saving some decent amount of coin, I would rather use OEM. If was putting in a new engine or something extreme (where I could be sure most of the coolant has been drained) I wouldn't hesitate using Zerex or some other aftermarket brand.
Lastly, I don't like to mix colors, because if I sell the vehicle one day, the potential buyer will likely see a negative in having an off color coolant. When you mix two different colors, you end up with a color that doesn't match any off-the-shelf coolant. If I were buying the car, the cooling system would be immediately suspect, and I'd want to look it over closely, more closely than I would if the system contained OEM coolant/color.
