Tried some on my spuds a few years ago. It was expensive and time consuming, just another of those faffy jobs I could do without. I think you have to do it annually and the funny thing is I can`t remember if it helped reduce slug damage. Thing is resistance to slugs depends on variety and every season is different due to weather and other varaiables in the micro world in the soil. I woudn`t bother again and prefer to rely on good soil husbandry.
Cheers
Pete 