I have to say I'm unimpressed that a Garda felt compelled to stop someone who was doing a u-turn, they then spoke to the driver who would have smelled of alcohol and they didn't do a breath test.
Gardaí can only breathalyse drivers, without the need to have formed the opinion that the driver had consumed alcohol, at so-called random checkpoints. Random checkpoints cannot, as one might imagine, be set up randomly but rather must be authorised, in writing, by a Garda Inspector.