The Marine Band Crossover is a modified version of the Marine Band Deluxe. Other than the graphics on the covers and the type of bolts on the cover, there are two main differences:
1. The Crossover has a bamboo comb instead of a pearwood comb. The bamboo is lighter in weight, has a slightly smoother feel, and has a different color/appearance. I cannot say with any certainty if it is more or less airtight – they seem about the same to me, regarding airtightness. Contrary to popular myth, the comb material does not influence the sound. You could swap the combs between a Deluxe and a Crossover and you would hear zero difference in the sound. All in all, I like the bamboo comb, and the harp feels lighter. I guess using bamboo is also better for the environment.
2. The temperament, or “fine-tuning” is different. The Deluxe is set to 19-Limit Just Intonation, while the Crossover is set to Compromise Tuning. The main differences are in the reeds of 2-blow, 3-draw, 5-draw, 5-blow, 7-draw, and 8-blow: these six reeds are slightly (about 5 to 10 cents) flatter in the Deluxe, whereas in the Crossover they are nearly Equal Temperament. (The 5-draw reed has the biggest difference). What this means in practice, is that the Deluxe sounds slightly warmer and more bluesy/flat, with slightly richer chords. The Crossover has a slightly brighter sound, and the chords sound a little less bluesy. The difference is very subtle, and most people cannot hear it. However, if you are playing in a band with other instruments, the Crossover can sound more “in tune” with the band. Whereas the Deluxe can sometimes sound just a tiny bit flat compared with the other instruments (particularly when you hit that 5-draw note). The difference is extremely subtle. But sometimes I can notice it, especially when playing together with horns.
Otherwise, the Crossover is a high-quality instrument and a joy to play. It projects loudly, with a rich and expressive tone. Having brass reeds, its lifespan is similar to most other Hohner harmonicas (in my experience, they start to drift out of tune after a couple years of intensive use). Also, the bamboo comb tends to accumulate greenish stains from the brass more easily than pearwood. This is easily removed using extra-fine sandpaper.
I prefer the Compromise Tuning of the Crossover and I also prefer the bamboo comb. However, the price difference between the Deluxe and Crossover is hard to justify. The Crossover seems a little bit over-priced, for what it is. (especially If you are building a full set of 12 keys).