Well I read the thread about one H'bird/2 locations and read this:

Parratt, I have the 899 and love it! I bought the model with the standard transducer (I think they all come with the standard) and then I bought the HD transducer for the unit. This way I have two transducers and I put the HD ducer on the stern and one on the bow on my Motorguide TM. Since I do all my scanning while at the yoke I use the HD to my advantage and then when I locate a pile I drop the TM and unplug the unit from the back an move it up front and plug it into a separate set of power and ducer cables. (bought the extra power cable as well for the unit to move up front).
Most people buy the 899 and send in the non HD ducer and exchange it for the HD for a fee of about $90. But to buy the HD out right was only $100 more than just exchanging it so I opted to buy.
Once I get my next unit I may get another 899 or compatible one with the ducer I already have or get another HD ducer. I will wait to see.
Yes it is a lot of work sometimes (you have to get two mounts as well which adds up) but I figure I can handle this until I find some money somewhere!
Hope this helps.