Uair is that kind of move that seems "out of the realm of possibility to use", but there are some viable usage for it.
It is slow & the Blade portion that starts first isn't really what people go for when using Uair, it's mostly the Beam portion we like more so baiting AirDodges & still following their air movement with our air speed+Uair does quite nicely. For one it's a anti-air aerial that out-ranges a lot of airborne Dairs except for some like Mega Man's hard knuckle & Robin's Elwind; the move can be great to punish landings on platforms or frame trap landings if they FF through the platform & land after we do, it's basically a grab. FH+Uair as Vanilla Shulk is okay, but we know how useful Uair becomes when augmented with Jump mode to chase off-screen / off-stage edge-guards near the blast line. Uair Uthrow to FH+DJ+Uair is a solid early Star KO.