I would call and ask them. I would assume (with no basis, so please check) that the melee (little stone in settings) are all little HOF diamonds. "Ideal" cut melee. Which would make them far superior to most melee used in 'off the rack' settings. Many of our PS vendors also use 'ideal' melee, some exclusively, and some only upon request. So if you are looking at a HOF setting, call them and ask about their melee on the setting you are interested in. If you are trying to compare the HOF setting to something else by another vendor, I would clarify the melee quality on that piece as well, just to make sure you are comparing apples to apples.
HOF has some stunning settings, and for what it is worth I've always thought their melee looked quite lovely.