I hear I'd get a lot more nutrition from sesame & linseeds if I could crush them. Is this poppycock or?

It's true, your digestive system doesn't do anything to the outer hull of for instance linseeds, so you just poop them out undigested.

You don't need to pulverize them, only break them open. And you don't need a gadget for that, a ordinary mortar and pestle does the job in a few seconds.

It might not digest properly because of the shell. If you just want to gain its nutrition and don't care too much for the taste, you could blend them into a smoothie with whatever your smoothie is. I'd imagine they should blend.

The amount of nutrition from sesame & linseed must not be exaggerated.

Yup, use a coffee grinder