I have used the Garmin motorcycle mount for over a year now - about 30,000 km - and am quite happy with it. No evidence of any problems with it.
I have not heard about the problems Burnie reported, although it is good to hear (from Burnie's report) that Garmin replaced the GPSRs involved.
I think that the Garmin mount should be more than sufficient for on road use (paved, gravel, whatever). If you plan to do really bone-jarring off road use, then maybe it might be worth looking at a more substantial (and more expensive) mount, such as the Touratech. You might find that you will also need an external antenna with some of the third-party mounts, because they obstruct the location of the built-in antenna in the SP 26xx.
PanEuropean