Can't you get the two units for an in-home trial? I'm sure you can get the Niagara; try and find a dealer (Puritan have an increasing US network) willing to let you try one.
As I've posted elsewhere, I found that the PSM 156 bested a Niagara 1000 and an Isotek Sigmas EVO3, among several other units.
As I've posted elsewhere, I found that the PSM 156 bested a Niagara 1000 and an Isotek Sigmas EVO3, among several other units.