John,
If I did this test above the thermocline, the sensitivity would have to be reduced dramatically which would take away from the target strength and some may use that as an argument, so I thought it best to do the test just below the thermocline.
My conclusion is that the Gen3 with the TM150 is a really great sonar match, not for CHIRP strangely enough, but for the higher fixed frequencies such as 105kHz.
The only benefit I see for CHIRP in shallow water, is when you are fishing from a stationary position above a brush pile for example, you will be able to track the fish better as they move through the cover.
Other than that, it's a deep water (>500ft) tool, especially with the high end CHIRP transducers such as the B175.
Hope that clears things up a little.
John Easton
Fisherman's Guide to Sonar
HighTec Fishing with John Easton