My experience with CallCentric:
a) It just works, consistently and reliably.
b) Without the drama and breakdowns that occur elsewhere.
c) CallCentric costs as a whole are pretty reasonable. And if my cost (depending on my options and usage patterns) comes out a couple of bucks more a month, I consider it well worth it.
d) Definitely, in Canada you have a cheaper option. If I were in Canada, I'd consider taking advantage of that, too. But the large majority of North American customers are in the USA, not Canada.
e) Neither klunky nor clunky, but rather crisp, functional, and elegant. That's subjective opinion, of course. I'm glad that you found choices that work for you.