I like that the Dolphins picked up a couple of extra 5th round picks and still got a stud offensive lineman. We'll see how he turns out compared to Fano or Mauigoa, but you can't complain about moving down 1 spot to pick up 2 extra picks. They can always use those guys to move up later in the draft to go after someone.
My thought on whether that is a good idea is purely contextual. If you have one guy who you absolutely love you should not make the trade. If you don't have a consensus pick, with half the room wanting one guy and the other half wanting the other guy, or a lot of guys saying that they like equally, then absolutely take the extra picks.