I spoke to a Twinfield representative a few months ago (Mr Terrar). It sounds a very good product except for one major drawback - there is no bank reconciliation option. It only accounts for bank transactions when they hit the bank account. A lot of businesses still deal with cheques with a minority (albeit a sizeable one), writing cheques and holding on to them for a week or two.
We were looking for an online solution for our bookkeeping but as Twinfield can't deal with this its not the product for us.