Finally had a chance to get the Cooper Creme Yvette, and tried making a couple drinks with it last night. I haven't yet tried the Rothman Creme de Violette or any similar violet-based liquors, so no real basis for comparison.
The berry (maybe blackberry or something similar?) notes are very strong in both the scent and taste. The color (using 2:1/2:1/2 oz) of the Blue Moon came out a lot pinker than I expected - very different from photos I've seen using the Rothman Creme de Violette... may try using a little less next time. To me, the taste of the Blue Moon was fairly balanced, and since I used a Meyer lemon (all we've got, right now), it would probably be even a little less sweet with a Eureka lemon.
The recipe I used seems pretty common, though some reduce the proportion of the Creme Yvette to 1/4 oz instead of 1/2 oz.
I also tried an Affinity, with the recipe from cocktaildb - it features sweet vermouth, dry vermouth, and creme yvette (1:1:1/2oz). To me, the resulting drink was a little on the sweet and syrupy side, but still pleasant. I think my dry vermouth is probably a little past its prime, which might be part of the problem.
Next, going to try an Aviation.