I know from flying this aircraft earlier that it takes about 30 seconds easlly before the engine will restart after running a tank dry in the air.
According to an article by John Deakin, where he mentiones some regs IIRC, the above would not meet current certification for SE.
I just checked the PA28 POH I have here and it instructs you to change to the proper (fullest) tank *after* having done the runup. That sounds indeed like a dangerous practice to me.
Yes; extremely stupid.