Are poppers better than a paper bag for making popcorn in microwave?
I have used some of the poppers which use "concentration disks" made by several sources, and will say I have had much better results with them than paper bags.  Popping time tends to be fairly consistent with much fewer unpopped kernels than a dry paper bag.  It only takes a couple batches to know what the popping time is for your microwave.  If time starts to increase or yield goes down with more unpopped or under-popped kernels, time for a new disk or your corn has gone stale.  It does cost more than paper sandwich bags, but with not burning batches and less loss and trouble, I personally found it worth it and probably a push on price.  And you need to make sure you keep a supply of the disks.  Usually it seemed 8-10 batches per disk before they would start to tear and need replaced.

I have not tried the ones which do not use the disks so cannot compare them.