Hidden vs non hidden chainrings
 

Looking at some after market chainrings and wondering what that's all about. Is it strictly a power meter thing?

Hidden chainrings are harder to install because you can't see them.

If you need help with chainrings you might post what crank you have and what you are looking to do.

Hidden bolts are a Power Meter thing, although Sram used a hidden bolt on their 5-arm Force and Rival cranks at one point; not sure if they still do.

Old stuff not as important today.

Not that it was really important during it's brief time.

Is hiding your chain rings a theft prevention thing?

The whole "hidden bolt" thing was a bid to do away with an arm on the crank spider because there was a crank arm right there that could do double duty.

Crank manufacturers did some math & have since moved on with asymmetric 4 bolt designs when they realized that the 2 closer sides of the "X" were all that was needed during the power phase of each pedal stroke.

The hidden bolt thing really doesn't have much to do with power meters; You can get power meters in about any configuration you want. It was to copy Campagnolo who happened to apply some thought to their designs.