I've got a Dean's Set from Schoolcraft which I believe came with an "unexpanded" shell. The unexpanded shell helps by allowing the face of the coin to look exactly like the regular coins. The shell sits perfectly on any of the coins that came with the set. It doesn't look like a little hat sitting on the coins.
I also have another set of coins which have an expanded shell (don't know who made it) that stands out a bit from the regular coins. I use this set to practice with sometimes.
If you're doing work on a table which should withstand the scrutiny of people watching from up close, then I'd go with a Dean's Set. I've been working for years with a regular expanded shell and some coins for a Roth-type coins across with success. The coins aren't side by side for comparison during my routine for more than a moment or two, so I'm not worried about anybody noticing the slight discrepancy in appearance. But when I work on a table for routines such as Matrix then I take out the Dean's Set. Hope this helps.