I feel that the new units have improved in quality as well as being less expensive.
I had an older unit at home that started acting up - it would alarm indoors but would clear when moved outdoors. I called the local fire department who came, sniffed the whole house, found no problem, and recommended upgrading the detector. The new unit (from HD) worked fine.
I like the ones with a digital readout - 000 is a good number, anything higher means something is going on. A second unit will either agree or disagree with the first.