by dat8962 » Jan 20th, '06, 18:37
I'd say that the only advantage, and albeit slight is that with the hopping halves you're left empty handed so in theory there isn't anything left to examine.
With the butter coin there are a few routines, such as coin through table that relies on you using misdirection to switch the coins (which is fairly easy to do by the way) so you can always hand out the switched coin for examination. However, routines such as rub away coin and restore will not leave you empty handed and you'll then find that the specs want to handle the coin so your switch will need to be invisible which isn't so easy if you're a beginner (although practice will resolve this but take some time).
As magicdoscoman states, if performed well then both are un-noticeable although in my opinion, specs scrutinise and have their own theories with all coin tricks. Not saying that they're right though.
From the two, my own personal favourite is the hopping halves.
Member of the Magic Circle & The 2009 British Isles Close-Up Magician of the Year
It's not really an optical illusion - it just looks like one!