I would say about 500W is a good limit to place on a whip like that based on diameter and the small corona ball on top. Short term SSB should be fine but long CW key downs could heat things up. You might even get away with short term legal limit but I would keep an eye on the corona ball looking for arcing.
I wonder how much surface area the contacts between sections on telescoping antennas like this. Seems like the multi-section shock-cord whips would be better in that they have consistent surface area at the contact point and the spring tension of the cord pulling the sections together. But, maybe not. Of course, you can't easily adjust the length of a shock-cord whip.
Chameleon has an antenna called the Tactical Delta Loop which uses 2 SS17's. They are rated for 500 watts per the manual. That's using the hybrid mini transformer not the micro. That's only 100 watts, but the SS17's are on both versions.