In my opinion the hard torpedo float (sold by Mako) works best for towing. You won't be able to pull it underwater like some of the lobster-style buoys dive flags/floats. I also own their large yellow inflatable float if I need something with more floatation. Also mentioned, it's very important to have proper scope out on your line.
I honestly prefer not towing a float because they do add considerable drag but they are helpful in high traffic boat areas or for mapping. I mainly tow one so I can capture GPS coordinates and track lines of my dives so I can get an accurate sense of distances and times involved for planning purposes.
This is about 2.6 mile roundtrip to visit a wreck offshore. I'm using a GPS logger (Navonics App) on a phone inside waterproof case that is securely attached to the dive float. It outputs a .gpx file giving me distance, speed and accurate times.
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