I've had good and bad experiences with GK customer service.
Dealing with Daniel Elliot has always been a pleasure, however, I had (note...had) a 210BLXII cabinet, just for rehearsals. (I know..this is the backline cheapie line.....but we're talking low volume basement rehearsals). I was using an Ashdown Electric Blue head with this cab, so it's not like I was pushing a ton of watts through it. It got used less than once a week, over the period of a little more than a year (so I was out of warranty). One of the speakers blew, I have no idea why....again....low volume, low wattage, but I emailed GK about getting a replacement. After a week, I got an answer from someone asking me to mail someone else. I did so, and a few more days go by. I was made the GENEROUS offer of obtaining a replacement driver for $90 plus shipping. Are you kidding? $90 for one 10 inch speaker of the cheapest variety possible? No thanks.
Having said this, I think their "non backline" stuff is really nice. I used a 1001RBII for my main gigging head for quite a while, and it had a ton of useful features, a great amount of power, and sounded pretty darned good.