I just purchased this in the last few weeks. I would say this. You shouldn't feel as though it would be funny to use coins from other countries as the trick itself uses coins from 2 different countries. One American Half Dollar and one English Penny.
You could use some patter about , you chose these coins specifically for their size because you want the transposition to be as "visible" as possible. Or because they are large enough so that the coins could not easily be hidden, in the interest of keeping it as fair as possible. There were two things that sold me on this effect. #1 was the fact that if you watch the video of Dan performing , it is exactly what you get , no funny cut scenes to disguise the "move" .. It is as plain as that , crazy visual and it happens in your hands exactly as it looks.
#2 was my Wifes opinion. I run effects by her first and if she is impressed by it from the teaser vid then I know it is something worth looking into. I say get it . The price is worth the coins alone.
Hope this helped , if you have any questions I would love to be able to help..