General consensus is that a properly located and installed thru hull will always out perform a properly located and installed transom mount, if for no other reason, it is mounted in "cleaner water".
That being said, there are some boats that are just about impossible to mount a thru hull on, and there are some boats that you can never get the correct angle or in the cleanest water with a transom mount.
The B60 has the additional advantage of not only being a thru hull, but does not need a fairing block to reduce the turbulence that is generated by a bulky transducer that projects far outside the hull. That fairing block adds to the difficulty of the install, can still create dirty acoustics and has potential performance disadvantages to your hull as well as making trailering tricky if not impossible.
I have a tilted element (B60 ) on my boat that replaced a conventional bronze thru hull. There is a much better image with the B60. I have seen or know of a number of boaters that made the same switch and got the same results. This is considering that the standard thru hull which was replaced was a rather simple single element, dual freq. transducer. You can not expect to replace a High Performance multi element or duplexed transducer with a B60 and get an improvement.
That dealer at the boat show is looking for the easy sale and is pushing the transducer that usually comes "matched" to the unit although the "match" is a misnomer. The "packaged" ducer is generally the most widely used model, that produces the best ALL AROUND performance under changing and different fishing conditions. It may not be the "match" for your particular style and areas that you fish.
The key to it all, is that no matter what fish finder you may buy, the transducer is the "heart" (actually the "eye")as to what it can do. Skimp on the transducer, or install one that does not suit your fishing needs and habits, and you will NOT realize all the performance that was designed into your unit.
You have already chosen what is probably the best stand alone fish finder on the market right now (585/620). For less than $200 more invest in the tilted element.
This post edited by Mad Mahi 08:49 PM 01/06/2008