The DSP-1 is now in my area. I picked up a bottle yesterday and had about an ounce or so of it. My first impression was that it's so close to the HH gold label BiB that I likely wouldn't question it if someone gave me a glass and told me it were so. The main difference isn't in the taste but the finish, as the Ritt has a nice, spicy flourish at the end. My second impression was that this would sell for half the price if the label said "bourbon" instead of "rye".
I don't have a DSP-354 to do a comparison. From memory, I'd say the 354 is a bit more complex but has more off flavors, like a wet cardboard taste that really puts me off. The HH Ritt has quite a clean, clear profile. I don't much like either of them neat, but this should do nicely as a mixer