What is wrong with OpenWRT/LEDE?
Some people have the view that everyone should have the freedom to control the software that runs on devices they own. If any compromises are made, then some of the benefits of Free Software go out the window. The OpenWRT/LEDE project does help give users more freedom than they would otherwise have, but some of the supported devices and packages are non-free.
how do I see if my device uses non-free blobs, etc? I mean as a user, not a developer.
For the kernel, you can run
if that shows an odd number (not dividable by 2), your kernel has a proprietary module. For firmware it's harder. You should find out if the binary blobs in /lib/firmware/ are actually used. Maybe the kernel log (dmesg) can tell.
And if it's used, you should find out it's source and license.
LibreCMC is just OpenWrt but without the blobs. If a device is supported by LibreCMC (and I cared about blobs), then I would use LibreCMC. If it is not supported, then it probably contains blobs that are needed for the normal operation.