Hi m8, I treated for whitespot earlier this month due to some recently added Clown Loaches using Protozin, even though I always usually use interpet products.
Protozin is a 4 day course which u use on the 1st, 2nd, 3rd, and 6th days.
I noticed whilst I was treating, that the clown loaches got worse with the white spot and I did lose 2 out of the 3.
I haven't treated them since, and 2 weeks later, everything is fine.
I didn't do any water changes before or after treatment, as we have utterly crap water where I live, so bad, the P.H tends to crash a day or so after the water change.
I think treating for whitespot is a bit hit and miss, depending on what species you are treating it for, and also the size and sensitivity of the fish.
As for treatment, I would go with the Interpet 1 if u feel comfortable with their range of products, which I must admit, I've found the 1's that I have used all excellent.