The main downsides/negatives to this technology, are basically politics, corrosion and being scared of nuclear radiation. Liquid Fluoride Thorium Reactors were created 50 years ago by an American chap called Alvin Weinberg, but the American Gov realised you can't weaponise the by-products and so they weren't interested.
Another point, yes it IS corrosivbe, but these tests of this reactor were 50 years ago, our technology has definately improved since then so a leap to create this reactor shouldn't be too hard.
And nuclear fear is extremely common in the average person, rather irrational though it may be. More people have died from fossil fuels and even hydroelectric power than nuclear power.