I have mixed feelings about them. I can never fully get my head around their balance implications. Being able to see through smoke and gas or other visual noise is pretty big, and to have such a big bonus you would think that the compatible weapons would have another drawback to bring them in line with weapons that don't have these attachments. For example the consensus that I'm getting from better players is that R-99>R-301 and Wingman>30-30 Repeater, perhaps even before the highlighting sights are factored in.
Whereas most of the time the game doesn't try to push certain legends toward particular weapon preferences, these attachments are technically less useful to someone like Bloodhound. And while most weapons aren't treated as specific legend counters, these attachments are very much hard counters to benefits offered to Bangalore and Caustic. If the DT is available at the replicator, it's a bad day to pick them.
I don't want to see these sights removed as I appreciate BR games for their chaos more than their balance but rather, I'd prefer to see more grenades/deployables/attachments that can grant legends the properties of other legends. Obviously I haven't thought these through in depth, but think in the vein of things like:
-Silence grenades (Rare, shorter version of Revenant tactical, probably not stackable as Fuse)
-Hologram. Single use item. Just like Mirage tactical but usable by anyone.
-Octane stim item. Combines Octanes tactical and passive with a slightly steeper initial HP cost. Regen stops once all health is refunded. Ineffective on actual Octane.
-Sticky camera. Essentially a throwable, immobile Crypto drone.
-Zipline kit. Do I even need to explain it.
You get the idea. If you look at the legend list you can come up with all sorts of items. If they rotated such things in and out between seasons, the devs could have more control over which legends are more/less appealing just as I feel these weapon sights do.
