In reply to Oscar Dodd:
Safe? Yes.
As ergonomic and enjoyable to use as Dragons/C4s? No.
From an incredibly brief google search a set of Dragons is £60 more than a set of Rock Empire cams.
When gripped on a tricky pitch, no one every though to themselves "I'm glad I saved £10 on this cam".
Four cams + four hexes gives you eight placement options, six cams gives you six. However, you'll probably find your hexes will be overlapping sizes with your cams.
It really depends what rock type you climb on most often as to what is useful, but either way you will make whatever is on your rack work.
When working and instructing I often take the three largest hexes on wire with me, when personal climbing I rarely carry them unless I know I'm going on an adventure route which needs a big and varied rack.