Your friend is partially correct (research first). Getting them established in the tank is the difficult part (research first). Fish stores usually do their share of damage before the coral is even purchased, so you would need to know what to look for in order to obtain a healthy coral (research first). They need to be handled carefully (research first). They need to be positioned properly in a proper environment (research first). They need to be fed in order to keep them from starving over the long term (research first). "Tremendous flow in the tank" may not allow the coral to extend and will definitely make it more difficult to feed (research first). If you get them established, they will need plenty of space to extend (research first). If they stop extending after 4-8 months, will you know what to do (research first)? If they start to bleach after 4-8 months, will you know what to do (research first)?
It would probably be a really good idea to do some in-depth research first before purchasing a "Green" Goniopora. If you do that, then they may not be so incredibly hard to keep.
HTH