Mostly troublefree, yes, but when Zen does screw up it can do it impressively. A week without any service after a service change they said I'd ordered, but I hadn't, and then being told "ooh, well, we have to wait 48 hours until we can raise a call" and "ooh, well, we have to wait 48 hours for a response", etc., and then towards the end of the week cancelling my service "as you requested", except I didn't. Zen definitely used to be much better, and they may well still be the best there is, but I get a "lackadaisical" impression when I have to make contact, these days.
Still a Zen customer, but wary.