All I can say is that I seen more of these furnace types lead to leakage and severe damage to the furnace that I can count over the past 35 years. You could not PAY me to put one of these on a furnace. I think htere are some that mount on the ductwork on the hot air side of the furnace. Leakage there is not as problematic or expensive.
From my experience, leakage in these occurs mainly due to people forgetting to periodically replace the water pad. Over time, the pad becomes hardened with water deposits and prevents water from flowing through the pad as it should. These pads needs to be replaced before the start of each heating season.
We need one, because our idiot landlord didn't put one in when he built the house. As a result, we all wake up with sore throats because the air is so dry. We finally resorted to buying little honeywell ones for each bedroom it got so bad.
I'm assuming you have forced hot air or hydro-air heat.
I'd stay away from the mist type that spray water into the airstream. Our builder installed one of these and it was a pain to get right, get the flow adjusted, etc. Once it was set up, it did its job, but we have very high mineral water (not 'hard' though) and we started to see scale downstream of the unit as well as a very fine dust in the house.
I replaced it with an Aprilaire bypass unit which we like much better. Since it is an evaporative unit, dust is not that bad. Maintenance is a semi-annual rinse and clearing the solenoid screen as necessary. Going on 8+ years.