In a couple of threads on GPS there were pilots who advocated that they led to lack of lookout, and were therefore dangeous.
While lookout is one of the most important anticollision devices in VFR, there were studies reported relatively recently which showed how limited is the effectiveness of lookout.
Hence the advisability of getting a radar service if you can, chosing an odd height, preferably not the one I have chosen, being hyper cautious near VORs around London, and while tracking between, and chosing the best Frequency to talk to if no radar is available.
Tempting fate, it is fortunately very rare that a collision actually occours, and I think most of those are in or near circuits.