Protecting our users ideas within our application.

Ideas are not unique and most professional investors would be hesitant in constraining their ability to invest in another startup with parallel (but not derivative) market. However, the conundrum is how to separate investors with devTeams who use the market insight (which is often the most challenging aspect) to leapfrog the proponent. Litigation is not the cut & dried decision you paint it as.

I suggest you just do the background check, whether investor has a stable of developers (conflict of interest), whether investor has a reputation of being a me-too thinker by asking what their investment thesis is and only screening for close matches (so quarantine non-pertinent ideas).

Frankly most ICT ideas are really not that unique so if the distinguishing factor is execution, better spend your time/energy on improving the success rate than arguing.

As has been mentioned, protection of ideas is a difficult area, and often litigation is going to be an expensive way of enforcing your rights, particularly if you are dealing with people located overseas. Generally though, having an appropriately drafted NDA is a great first step. The important part, though, is doing your due diligence on your investors. Do you really know who they are? How would you sue them if you had to? Let me know if you need advice!