I'd be very wary and it would make me immediately look at the other houses in the area to see if they had similar security measures. I'd also do some net research and ask other home owners in the area if there was a crime, vandalism, anti-social behaviour problem?
Essentially there are four possibilities and you need to nail which one it is
1. The area has a problem with crime of some description hence the counter measures. This is a problem for you.
2. The owners have a particular problem with crime for some reason. ie. current occupier is well dodgy and fears a straightening knock at the door. This may be a problem for you.
3. The owners are paranoid worriers scared into hiding at home by the Daily Mail. This is not a problem for you as long as you steer clear of the Mail
4. The owners are fucking weird pavement pervs like Mouth. This may be a positive for you if you are similarly inclined.
You need to do some research to establish which of the above apply.
Hope that helps