From what I understand, the Orginal Waterlox, which they now also refer to as the "Original Sealer Finish," is the same as the "Marine Formula" except that it has been thinned (by ~50% IIR, but don't hold me to that) in order to...
- make it a wipe on finish (e.g. no streaks)
- allow it to soak in a bit quicker, deeper, and easier
So when they suggest a "sealer" before applying the Marine Finish, what they are recommending is a coat or two of their Original Sealer Finish followed by a coat or two of their Marine Finish.
You can achieve the same result with just the Original Sealer Finish. It will just take more coats to get to the same film thickness.
I used to use Bloxygen as well, then discovered that cans of keyboard "Dust Off" air spray also work just fine ... and cost about 40% less.