I got a small slice of grief off the traffic cops for my JDM plates - both ends - because the text wasn't the right size. Fortunately, they were joking (I was out doing an operation with them at the time, as you do).
I pointed out that I couldn't fit the right size of text on the plate on the back, but it did kind of sway me to get a standard Euro-size plate on the front. Plus I like my number-plate surround thingies. Unfortunately the local Honda dealer in Hungary closed down before I could get surrounds off them, but I kept the Toyota ones in memory of my many Celicas.
So it's a no vote for me on the front, but I much prefer the JDM on the back.
A sticker number plate on the front bumper is always an option ...