I've heard that dedicated NICs like that are a waste of money that don't provide enough performance boost to offset the cost and extra power consumption.
But that's just what I've heard
You've heard right. Unless you just want an expensive new toy to play with, I wouldn't waste your money on one. They are cool and do offer benefits, but for an average user, even a gamer, they are meager and a headache to derive any real advantage from.