Agree with points made above. A little chirp or two, especially if its a bit windy I would be okay with. If it was going off continuously I would be telling my friend (hopefully before the speed got THAT low) to check the speed and if he didn't remedy it I would take control.
teknow, I don't agree with those things that have been drilled into you, but I have never flown a Tomahawk. In general though, fly a proper speed, don't bank stupid amounts, and don't let the turn slip or skid. Those are the main things I would be concerned with. More than 15 degrees of bank I don't see a problem with (unless you're too slow and/or uncoordinated) and do it at a height that is appropriate to how tight you are doing your circuit. Flaps again I don't know for the Tomahawk but I see no reason to restrict their use on a 152.