I don't have GV (unavailable in Canada without some work-arounds). I haven't used the Hangouts dialer much, but hey - free calling anywhere in Canada and US is cool. Free is good. I find the connection not quite as good as an actual cellular call (although that could be my sometimes-sketchy satellite internet connection), but it works.
I think the biggest advantage of GV is if you often switch devices or carriers - having one number to give out would be a seriouos advantage. Other then that I haven't looked into it at all. Partly because I don't see the advantage for me - I don't make a whole lot of calls - and partly it's just not available to me. No point for me to investigate any further. Maybe someone else can give you more information