You just have to ask or find out how thick the foil is. If you get the low density coating of aluminium similar to what the party balloons have then you won't get any long shelf life from the bags as they have pinprick holes in the foil layer.
The mylar alone won't get you anything, so its the thickness of the foil that gets you the protection.
So yes, the hop bags in the shops are commercial foil bags. And nothing stopping you from reusing them if you remember to keep them in a drawer after using them to build up a nice collection.
I now have to find a good source for decently thick foil lined commercial mylar and should be set once have both those and the sealer. One batch to run the imported hops and one to run this years hopeful hop harvest from the garden (almost six times as much money invested in the garden hops in rhizomes and soil amendments, lets hope I can get some yield!)
Cheers,
Brewer Pete