I am not sure why directbet is D tough, is there some sort of complaints and scam accusations towards them or do you think they are bad in general? They are one of the oldest and most wagered sportsbooks I have heard of and I would be interested to know why are D and not C or B let alone A.
Now that books are processing payouts so fast, DirectBet lost their advantage of not needing an account. Their odds are bad, may be the worst, and they've confiscated money from approximately 6 players. Not only are winnings confiscated, but the bet amount too in a couple of cases. Bet confirmations can get delayed because of the system that they use. A bet may not get confirmed/rejected until the game goes final.