I got my energy audit a couple of weeks ago and #2 on the hit list is to replace my NG water heater with a indirect tank type water heater.  I swung by a small wholesale place the other day and he gave me a pretty attractive quote on a "Bock SideKick".  I don't know much about them but the specs look pretty good compared to the Amtrol boiler mate. 
Has anyone used one these?  They look well made and weigh about 100 lbs more than the Amtrol for about the same capacity and the amount of recovery looks significantly better than the Amtrol, 1.5" internal coils etc.
Thanks in advance.
Jim