I have used a few G5RVs over the years and believe that their simplicity, more than their performance, accounts for their popularity. In my experience it is very difficult to adjust the two available parameters flat-top length and matching line length and end up with good SWR performance on many amateur bands. That being said, I have achieved a 5:1 SWR on most band and find that is low enough to use low loss 50Ω Coax if the runs are short enough. As Varney recommended, a tuner makes life easier at the radio end of the feed line.