I used the grooved board with pretty good results. One guy forgot to secure the loco snugly to the board so the weight of the loco allowed the engine to slam against the end of the box and bent the pilot. OMI Standard and Veranda Turbines are notorious for this kind of damage if they are not secured to a board.
Recently I was educated to another way of wrapping/shipping that is definitely more of a PITA, but just about guarantees no damage. It cost more because you will be shipping two boxes, instead of one, but it's worth it to me.
Wrap the loco in multiple layers until there is 3-4 inches of protection around it on all sides. You can use tissue paper for the first layer to protect the paint, surround that by several layers of foam wrap and then multiply layers of small bubble wrap for the outer layer. Place this cocoon in a larger box surrounded by peanuts. Do the same with the tender if that applies.
You then ship the loco in one box and the factory inner box in another. The inner box just needs to be protected from dirt and handling chafing so it doesn't need a lot of fancy wrapping.
Some of the importers are building some pretty incredible inner model boxes these days (Key, Kohs, Etc.) for their latest production models that might not require going to this extent. Generally a factory packed model is good to go, but once unpacked they never seem to get packed that way again.
But, it all boils down to the skill and care the shipper uses to box the locomotive up. If they only use the worn out factory packing and figure that's good enough it is up to the train gods if it will arrive undamaged. Nothing like waiting years to purchase a model only to find it damaged due to a careless packing.
Butch