Absolutely not a personal item!
A personal item is defined by most airlines as a handbag or a computer bag or a bag of similar size. The Keepall 45 counts as a (smaller) carryon bag. Now, you might be able to get through as many airlines are lenient on longer flights with larger aircrafts and have different rules for Business/First passengers. I am sure in most cases, you would be fine. But it still does not make it right! Keep in mind that weight is an important component of carryon luggage allowance.
FYI: as someone who travels quite often, nothing drives me crazier than passengers who abuse carryon luggage rules. It adds up quickly and always ends up being a huge headache for the entire cabin. Don't be that person!
I always felt that if it fits under the seat it's a personal item? I've never had to store it in the overhead and I don't fly first class. I've brought mine on at least 18 flights since buying it last September with no problems. I agree though that those that abuse the overhead space are annoying. I blame the airlines for that though.