michael,
as far as I remember – the latest builts of bitvice encoder have the purifer-allgorithm built in – but not the whole options.
I discussed this with roger from innobits a few times.
my advice is: if you would like to downscale from HD to SD use purifier, because it is doing that VERYgood.
it could do real good upscaling as well (for example from anamorph HD-formats to the square-pixel-ones) 1440 vs 1920 or 960 vs 1280.
it will take time to do so, but it´ll have an incredible quality – purifier is worth the price.
cheers
danny