Very sturdy, comes with all the machine screws and washers and a hex key you need to mount it to your stand. Using stands designed for screens gives me so much more flexibility in positioning the speakers in the sweet spot while also keeping them off the desk itself, which not only saves desk space but also reduces reflections.
I used them for my 8010s and one thing to note is that once they're mounted you can no longer access the dip switches or the power button on the monitors. You must unmount the entire monitor from the VESA plate and also unscrew this VESA adapter completely. It would be nice if there was an opening in the centre of the adapter but I suppose that might negatively affect its structural integrity. Also, this might only be a problem for the 8010 speakers being the smallest size of Genelec's monitors so your mileage my vary.