the metal tint will effect the AM radio reception the most (low volume, statics, etc ) but it will also reduce the pick up of FM stations quite a bit as well.
in my BA ute with carbon tint i can pick up the local FM stations clearly for 100KM or more out of town and other poeple with metal tints on their BAs say that they have to change stations after 30 -40 KM .
the LEGAL limit for window tint is actually 35% visible light transmission and 10% refectivness.
35% films can vary a lot in apearance with some looking very light and others much darker.
on a black car with dark interior the window tint will look a lot darker as well.
metal films have more of a shine / reflectiveness to them so on the black car will stand out more than a none metal film. ( i would steer clear of dyed films as they mostly fade and turn purple )
high quality metal films will keep out a bit more heat than the carbon film while plain dyed film does bugger all.
most tint will stop 98 -99% UV
my rcomendation for a metal tint would be the 3M Scotchtint SP/CS black metal 35 or Solar Gard Quantum 38 . both are very good films backed be good companies.
my personal preferance for looks on a black car is still the 3m carbon black scotchtint film, it has the blackest colour of any legal tint , is gaurenteeded not to change colour , has very little reflectiveness, very clear to look out of.
it is avalabe in T35 (legal) or T20 (NOT legal)
the lower the number - the darker the tint.