I bought this as an expansion for my Alesis Command Mesh Kit, and it works really well. The frame for the Command kit is slightly bigger than that of the Nitro, and so I bought a couple of larger drum clamps to fix the tom and cymbal to my frame (the clamps supplied are, quite naturally, for the Nitro and so too small for the Command, but that was to be expected and not a problem).
The tom and cymbal work really well, and it's worth noting that the current product description is slightly wrong: the tom is a dual zone pad, (the same as the ones that came with my kit - the only difference is cosmetic: black rather than chrome), and the cymbal has a choke (identical to my existing ones).
Nothing not to like - this expansion kit works perfectly.
A quick hint to anyone using the Addiction Drums plugin: set up your midi mapping to Alesis DM7, it matches exactly :)