I should have added the obvious debate but you are probably aware that all of these sytems depend on other aircraft squawking, and squawking mode C or S if you expect to "see" their relative altitude.
Many aircraft do not have a transponder.
Gliders use an entirely different system (to the extent they use any electronic means of collision avoidance) - FLARM. FLARM will not be seen by any of the systems you mention and therefore if you wish to detect gliders using FLARM you would also need to buy this as well.