Garmin echo ap 50s vs 551s

I was thinking of buying a garmin 551s now that the price has gone down. However, when I went to look on the net I spotted the new echo map 50s at around the same price. It seems to have an updated fishfinder and GPS and includes a transducer. Does anyone know anything about this. I am afraid that I have missed some obvious reason why I should not buy the 50s. I am not sure if it. Includes the same free maps.

Yes the 50s would be the dogs!
Not sure, but I don't think it is available yet.