Alum heat exchangers are good for heat transfer but it ends there. Weil, Buderus taught alum hx's. Weil started including what I call magic potion with the boilers. It basically coats the inside of the hx to help slow down the corrosion process. Buderus has also seen leakers. Burnham is no longer offering the Freedom which has an alum hx.

I would take a look at the Viessmann Vitodens 100. Its a simple no thrills condensing boiler that will provide 95%AFUE with a limted lifetime warranty on the hx. 10 years full and then 90% after year 11. It's basically the same warranty as a traditional cast iron boiler.

Its a great boiler for fin tube jobs. That 60K sounds a little high for a 1,500 sqft house. I would ask for a heat loss be done of the home. Heat emitter measurement is also necessary to be match to the loss so you can set a heating curve.

Sold hundreds of Vitodens in the past couple of years. Avg fuel savings is 35-50% if properly installed and set up.