I'm new to this forum, but not to the lawn and garden business. Having been in it full time since 1998 as a lawn and garden chain manager in Savannah, GA...there is no major problem with doing it from the ground, depending where you are located. I find that doing from the round attracts major unwanted rodents & snakes.
Plus one major reason I personally like using a compost tumbler is because of it's ability to mix the compost often for an even mix and being able to keep it contained so no unwanted pest come around. I also mix in a compost starter with my piles because it helps start the breakdown process. One last thing guys, the temperature is really important in the process of compost coming out right, it should be steaming and a dark brown or black when its done. Make sure to choose a well insulated compost bin or tumbler if you choose to go that route.