I would like to see what type of device respondents took a survey on. Is the figure shown in results overview reliable?
It is fairly reliable. A better way to see what devices your respondents are using is to export a csv file and review it in MS Excel (http://help.surveygizmo.com/help/article/link/excel-export#what-does-an-export-look-like-). This file includes a field called USER AGENT that details the respondent’s operating system and browser.
Sometimes this information is blocked if the respondent is connected to the internet through a VPN, but the information is usually good enought to give you an indication of how your respondents are linking to your survey.