Fk hubcentric spacers arn't anything like that mate, lol, I've got them too.
But, you've got the spacer (which I may add is alloy, and perfect balanced) which is bolted to the hub, then the spacer has a collar on it to act as a new hub for the wheel to sit on, which is then bolted, in seprate bolt holes, to the spacer.
It's as safe as a spacer could be tbh, the above, not so much, but then my spacers were £90, these arn't lol.