I have found redemption on GP Partner airlines to be the extremely easy. Often easier than the larger FF plans. Just phone Avianca, Aeropostal or Taca and make a reservation. Call GP and they issue the ticket - no worries!
Now KLM is a different story. But the issues with KLM are not unique to GP. I am a member of KLM FD and it is insane to try and get mileage tickets from their partners (MH / Jet Airways). It is the phone / fax / phone / call bacl next week scenario. I think that what we are upset with is not GP but the archaic way KLM alots mileage seats to their partners.