I have a 55# longbow (see my signature). It is quiet and seems plenty fast to me, though I don't care all that much about speed. It blows arrows through whitetails pretty easily. The nature of a mild r/d tends to give a bit more shock than recurves or radical r/d bows, but my Mahaska isn't all that bad. I use a 14 strand B50 string, so that probably helps. It shoots right where I'm looking, but the 55# makes it less fun to shoot than my lighter bows, so I don't shoot it as often as I once did.
Like any bow, some will love them and some will hate them. My hunting partner hates Black Widow bows. Does that mean they are bad bows? Thousands of happy BW owners would say no.
Most of the people I know who complain of shock just don't know how to grip the bow properly. A locked elbow and a tight grip will make a bow feel shocky. Also, shooting lightweight arrows doesn't help either.
I prefer my Kanati, but not because of the handshock. It is shorter, handier, and the lighter draw weight makes it more fun to shoot.
Before you decide, shoot some Mahaska bows yourself. Don't take my word for it, or anyone else's either.