There a lot of questions that go into the decision process. The big one is how do you plan to use it? Supplemental heat? Backup heat during a power outage? Ventless? Direct vent? Stack vent? Efficiency? Fresh air intake?
I have one in my great room, provides backup heat during power outages for my in floor hot water heat, vents and draws fresh air through the roof stack, is about 85% efficient. My in floor heat is 95% efficient.
I use it prominently in the spring and fall to heat the house. Once I turn on the in floor heat I reduce the thermostat setting on the fireplace and use it as backup heating.
My wife love it. Good luck on your decision.