CO Alarm: Kidde Nighthawk vs. American Sensors

Over a year ago I purchsed a new Kidde Nighthawk Premium plug-in CO detector (Model 900-0076 AC) for my house. Initially it seems to work fine, but after several weeks it started giving single beep every hour or so.

At first I thought the battery was dead so I replaced it with a new one. It didn't help.

So, I called Kidde who, based on the error code on the LED display, immediately sent me a new unit (didn't even ask for the defective one to be returned).

Then the story repeated itself after several weeks. I called Kidde again and again they sent me another new unit.

Then the story repeated itself after several weeks... At this point I gave up on Kidde, realized that they have an inferior product marketed cleverly and decided not to buy any CO detector for the home until I find something that I am convinced works (I used to have the excellent AIM

but when its battery died before the 5 year warranty ended, I discovered that the company went out of business).

So time went by (and we are still alive) and I discover that finally there is some home for a better alternative: Model CO851 by American Sensors.

The marketing for it says "Voted top alarm in the USA!!!" - and it sure is priced higher than the Nighthawk - but before going ahead and purchasing it, I am curious to know whether anyone here had experience with it and if so, does it really live to its expectations?

I also just found the following interesting article:

and wondering again: Have I found the best carbon monoxide detector in the market?

Thanks! Sam