That is a beautiful dulcimer. He is a good luthier. You ordered the spruce soundboard, and they are brighter than red cedar as he states. As for Jumbo, that is simply a statement in reference to other models.
I’ve got my new dulcimer
I went and picked up my new Black Mountain Instruments Jumbo 81D with case. It is a beautiful dulcimer and looks to be well made. I was surprised to noticed that the dulcimer didn’t closely match the dimensions listed on the website but I’ve decided it doesn’t really matter for my purposes. It seems to be easier to play than the loaner kit dulcimer I’ve been using. It has a bright sound with good volume. The treble is a bit weak on the higher frets which is to be expected with a larger dulcimer. I’m looking forward to getting used to the new fretboard and the double melody strings.