This depends where you are giving the exam.
If you are giving the exam in your own school, it would be in yout best interest not to take that calculator as it is not allowed in the O-Level.
However, if you are going to the exam and it is being conducted by the British Council, then take any calculator. Calculators are ignored here, because there are so many people taking the exam, the council does not have the time to check each individual calculator. However, if you are caught by any random chance, my some overbearing local examiner, you will be disqualified for the examination.
In simple terms, if you are giving the exam in your school take a calcualtor that is allowed. If the BC, then take whatever you want, there is little risk involved.