Also remember that the "life" of the protect is 7 years, so after that 7 years the protect has to go in the bin and you have to replace with a new one, just as you would a normal smoke detector....but they're much cheaper and often have a longer life cycle. I've read things of people installing 5+ of these in there house at the same time, I think i'd cry on that day in 7 years time when I stick them all in the bin and have to go out and buy new ones.
I'm not sure what the issue is with the protects, but I've never had a false alarm off any of the normal smoke detectors in our house, so quite why they seem to have to many issues.
I thought they looked pretty neat, but thought better of it when the people I know with them were living on their wits end because the bloody things keep going off!