Now, upB's hitbox and frame data is perfect for ensuring beat-outs or trades, but in my experience, I find that one of the best ways to hit the spacees, especially Fox, OoS with upB is to actually
trade with it on their aerial. Why? Well, the spacees get flung up in a good bit of hitstun from even just the first hit of upB. However, Samus usually can't take advantage of it because she is going through the entire Screw Attack motions herself. By trading, Samus gets knocked out of the upB animation early with minimal KB and the spacee is still flung up into the air, leaving Samus completely free to follow up.
I personally actually aim for trades for this reason sometimes when I know the opponent is going to dairshine and it works!
If it's Fox, Samus gets knocked lightly out of upB and has all the time in the world to retaliate. If it's Falco, at low %'s, it's the same as with Fox but with a little more hitstun for Samus, and at mid-high %'s, you just have to make sure you tech the ground. This 'cancelled upB' combos into pretty much
anything way more reliably than the full upB does.