Totally agree with warped factor.
I think you should call clear prop clearly and loudly then wait at least a couple of seconds for any reply. I don't feel at all embarassed and indeed I relish it. (The passengers love it too)
The instructors who poo poo it may work at airfield with good security where members of the public are not wandering around.
However anything could have got near the prop as you start. Remember you have been heads down for a significant time before starting and an engineer or a small child could have got in the way. Anything that reduces the chance of that prop hitting anything has to be good.
It also warns people behind you that a big wind is about to hit them. A couple of second gap may be enough for them to prevent being knocked over.
Long may it last.