Wunderwaffe does not mean it’s a great weapon, it just means it is portrayed as so in a way that helps in terms of propaganda to make it seems as if with X or Y weapon the war would be won. It was a trick employed by the Nazis, and in Ukraine it was already done multiple times, first were the HIMARS, then the Leopards, now cluster bombs, and so on.

Using munitions to defend your own land compared to attack the enemies land have enitely different moral connotations.

The main issue with cluster weapons that makes them so controversial is that they tend to have a high failure rate and leave unexploded ordnance (UXO) that will sit around and remain potentially dangerous for years (parts of Europe still have issues with unexploded WWI/II bombs turning up occasionally, Vietnam and Cambodia and other countries affected by the Vietnam war have issues with it, etc.) The bomblets from cluster munitions are also small, we’re not talking something the size of a car or even a suitcase that would be pretty obvious sitting around out in the open, they’re often about the size of maybe a softball or an (American) football that could get lost in some tall grass or rubble, and is also a pretty good size for someone curious (a child, perhaps) to pick up and mess around with.

Russia has already been planting mines and using cluster munitions extensively, so even if Ukraine didn’t use them they’d have a pretty extensive UXO cleanup ahead of them. That’s also not the case though, because Ukraine has also been using cluster munitions already, of much the same old Soviet designs the Russians have been using so that cat is already way out of the bag. These old Soviet designs have a pretty high failure rate, the newer us-supplied cluster munitions should be more reliable and so leave less UXO to be cleaned up in the future. Since they have already made the call that they’re going to accept the long term cleanup of using cluster munitions, it’s probably best that they at least use the better ones.

Ethically, I think there’s a definite argument to be made that it is more acceptable (though not necessarily making it right) to use them on your own soil in defense, than it is to use them against an enemy on foreign soil. It would also probably be expected that they will use them more judiciously than an invading force would since the cleanup will be their burden to bear, likely for years or generations to come. Ukraine can make decisions that will affect the Ukrainian people, Russia should not, nor should Ukraine make decisions for the people of Russia.

I won’t pretend that I like the idea of cluster munitions being used by either side in any capacity, but I think it’s Ukraine’s call to make in this case. War forces people and countries to make uncomfortable decisions. Cluster bombs are effective, and their use could potentially help Ukraine reclaim their country faster. Whether that’s worth the long term collateral damage is tougher to say.

Presumably because that’s where the battlefields are. These weapons are very problematic in civilian areas. On the battlefield they’re just somewhat more affective form of artillery.