Yes, the sound is different. The weight is also very different - When you pick them up you feel the difference in a second, I sold a Flexmark that felt like half the weight of my silver labels. In fact, I did a drop test and it fell to the ground only slightly faster than a latex balloon. (j/k) Also, Lexy put those fixed twizzle cords on some of them that are one step above a phone cord and are frequently screwed up even when you open a NIB model like I did.
They are all good keyboards, but I much prefer the earlier models and they are not all the same.
I've never used a Unicomp yet, so I can't comment on them, but I can comment on the incredible build quality of the 1390120