It actually depends what the track is made from

If you asume its made out of a plastic with no flex then it probably wont flex much haha

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I can tell you that this setup allows for a lot more flex than with a regular pack of inserts in which flex is non-existent. The only way you can get flex with regular inserts is to have them separate, in which case they will pull out easily.
I think this idea is good for wakeboard/ twintips, it saves weight, adds easily changeable stance between many different boots and baseplates and allows for flex directly outside of where your binding ends.
The only idea I don't like is the stance possibly slipping and changing (however I haven't tried it yet so I don't know about that).