I've had plenty of experience of hand augers when I used to sample soils for testing. As smud6ie suggests, they're fine in good quality soil or even clay, with it's smooth consistency, but one you get stones in the mix it won't be pretty! It will also be very hard work - the ones I used were a lot smaller diameter and they were difficult enough.
Wood in concrete is OK until, a few years down the line, the bases rot and your left with the problem of getting a large concrete block out of the ground, followed by a huge hole requiring even more concrete to replace it.
Metposts can be OK, but what about a good old fashioned sledge hammer to bang the posts well in? Or an easier option - a post hammer (like a heavy metal tube, closed at one end, with a long handle running down each side - you simply sit it over the top of the post, and bang it up & down)