I actually thought the same thing at first. I've met alot of people who have kept the 3 fish together successfully.I don't see that working out for too long. The flounder and gobies are brackish while the puffers are fresh. Also the puffers will probably kill the others before long. Good luck though
I housed DP's with several different species of fish with no issues at all. Including Halfbeaks, guppies, and a few others. Sometimes it will work out, you never know till you try...just be prepared that it might not.