They have quoted a mid efficiency, 75,000btu cast iron, gas fired hot water boiler. Utica has been around a long time, use parts that are readily available and affordable, and last a long time. 84% efficiency is not unusual, and is accomplished by using a vent damper, which in my experience is the most vulnerable part on it. It has an emergency or bypass switch which is great if it malfunctions. Most manufacturers in this range use a similar setup.
Good boiler for the money. They have a very informative website. Up here in the frozen north they are quite common.