I only use it to help hold together some complex assemblies when putting them together so I can't speak to it's strengths, but:

> Do you need a conductive substrate on both sides to apply the release voltage?

Yes, you attach VCC to the substrate you want to remain bonded and GND to the substrate you want to detach.

> How available is it for purchase if you aren't Apple or Samsung?

You can just call up your usual 3M distributor and request it. It's over $2,000 for a 100 meter roll so it's not something you'll usually find in stock at your local Grainger but it's not some super-secret material only available to the biggest manufacturers.