The starfish is from tritech, which is a reputable company in the marine technology business.
The starfish operates at a very high frequency, 475khz, meaning the range will be limited compared to other professional sidescan units. The beamwidth of 1.7 degrees is poor compared to professional units that usually have a beamwidth of less than one degree, meaning the focus and resolution of the images is degraded from a professional quality unit such as GeoAcoustics, EdgeTech etc.
100 meter range per side is possible at this frequency, but that will definitely be the limit. In many water conditions the range will be somewhat less than that number.
However, the price is extremely low. This is a case of 'you get what you pay for'.
Keep in mind that you will need to capture and process the data from the towfish. Ask what, if any, visualization and processing software is included.
Ciao
P