In this context I think it's fine. Russia has already been using cluster munitions on Ukrainians and I doubt the AFU will be as careless and cold in their use as the Ruzzians. Unexploded ordinance is a genuine concern, but the lands being fought for are already so heavily mined its almost a moot point. Just my 2¢
Yeah, I'd obvious prefer cluster munitions not be used at all, but thanks to Russia that cat is already out of the bag and whether or not Ukraine starts using them they're already going to have a big UXO cleanup to deal with when this is over, and since it's their country I imagine they'll probably be a bit more judicious in their use and it's kind of their call to make if they want that on their plate.
If they start making moves on Russian soil with them, that's a little murkier ethically. There's definitely an element of "turnabout is fair play" involved but I wouldn't exactly have the warm-fuzzies about it.
It's crazy to me that we are talking about a counter-offensive. Last year we weren't even talking about a defense at all. Way too go, Ukrainians. Give 'em hell and send back these bastards at home once and for all.