I've tries vinyl from Rtape (fx range) and my experiences were very bad.
Never seen any material that curls so much, OK Rtape says to use coating pen on the edges but does not works so much, prints not not stick after few weeks. My provider told me not to print near the borders, great solution when the design does not allow it :-(
Tried silver, gold and red all with same results, also tested many print conditions (ink rate, temperature etc...)...
All my customers complained about it after only few weeks, even those who I made decals without print (juste dye cut decals) or those which I place transparent printed vinyl on it. I use metallic vinyl quite often.
So my experience with Rtape: curls a lot and glue is not sticking well, the color range is wide but providers in France only resell a limited color set which make nonsense to buy this media.
For silver and gold, I went back to oracal 352 which is great but limited color range (new color coming: pearl white looks great). Still looking for blue, red and orange metalic vinyl...