I wasn't sure about spending more money on a two-tier synth extension than I paid for the K&M 18990 Rick stand, but it's a worthy addition given it's build quality and tweakability.
Pros:
The extension wasn't difficult to assemble, albeit a little time consuming adjusting it to suit my setup; however, this process only ever needs to be done once as the arms are easy to extend/retract.
The sockets fit perfectly onto the K&M 18990 stand, and I experienced no inconsistencies with the angle of both slopes.
Cons:
The only issue I had was that the replacement rubber caps, where the groove to make more space on the base stand for the extension were too narrow to slip past the support bars, but this was very easily remedied with a stanley knife by extending the groove.
Overall, an excellent complement to the K&M 18990 Rick synth stand; I definitely recommend the pair.