I have one similar to this..It works pretty good, but I believe you're looking for digital interference. My counter will not pick up digital, it will however indicate the presence of an rf signal and the frequency numbers will roll never indicating a given frequency. If you know a ham radio operator see if they have one you could borrow.
Ideally it would be nice if your RC Club or Group could beg or borrow the use of a spectrum analyzer which covers the 2.4 GHz band. The main issue is that there is so many types of signals crammed in that band Even with a spectrum analyzer you need someone familiar with the signals to discern what should and should not be where it is. Google can likely bring up the range of frequencies and how those frequencies are actually designated.