Its enjoyable and I do like the challenge of trying to hatch a Mercenary egg, on the account it gives you that pleassure of achieving something, while those who have pre-paid cards uses points to get the non breakable eggs, just ruins the game and sell those eggs with ridiculas amount of in game money...Like 2 million for just one mercenary egg @_@
If you want my opinion? Getting the mercenary eggs aint the hardest to get XD They drop at pretty good times, its the hatching is where the trouble comes. I remember grinding for atleast 5 Renamon eggs in two days (I don't play the game all the time, since I have other things to do)
Now people will say that 4/5 or 5/5 sizes is your main goal. But that in itself is hard, on the account your Egg will...well break when every time you give the amount of data during the process, especially around 1/5 and 2/5.
But anywho, 4 out of five Renamon eggs I finally got a 3/5 Renamon. Which I did a little test couple weeks ago, to see how many eggs usually hatch for me XD And it seems around 4 Digimon eggs, they will hatch for me around 3/5 ^^; but any higher they will break on me XD