I am very new to the hatching game, so this is just an amateur opinion based on my experience. We recently decided to add to our flock and went with hatching eggs. 15 of the eggs came from our hens and were simply carried from the hen-house to the incubator. Also placed in the incubator were 16 guinea eggs that came from a friend's farm about 10 miles away. These were carefully packed and driven over. 33 additional eggs were ordered and came through the mail. Here are our results: all 15 eggs from our hen-house hatched beautifully on day 21 and all are doing well. All 16 guinea eggs hatched in a 24-hour period beginning at the end of day 26. All are healthy and happy keets so far. Of the 33 eggs that came through the mail, only 11 hatched and survived. Of the remaining 22 mail-order eggs, 13 never developed chicks at all, 4 had chicks develop in the eggs but never even began to hatch, 3 started hatching but died before they made it through the membrane, and 2 hatched and died within hours. These eggs came from a reputable supplier, were packaged beautifully, and I have no doubt that they were good, fertile eggs when they left to begin their journey via USPS. Based on our experience, we will not be ordering eggs again unless they are close enough for us to pick up in person.
Hope your flock addition goes well in the spring!