I think hot water is even better - I think you have more control over the temperature and more even heating. Oven=melted plastic (at least in my mind). I know, the oven is supposed to be turned of before the procedure, but still . . .
I was following instructions I read somewhere. Used an oven thermometer (not the knob on the stove) to determine temperature. Max temp was 100 and something F (forget exactly, would have to look it up, but was hot enough to soften styrene but below melting temp). All I can say is that it worked. YMMV.
I can see water having advantages as well. I have flattened some resin pieces in the 140 F water out of the tap. As you say, easier to maintain a given temp.