It does state
Fit Note: (This Kit Contains A Combined Bellows And Bump Stop; Kit May Be Either Old 1 Piece Or New Updated OE Style 2 Piece).
So you wouldn't know what you'll really get. And it says "updated" so I'd think that any updated design is better.
I also prefer the 2 piece. If the boot tears before the bump stop breaks or vice versa, you'd only have to replace one or the other.
Also preferred if the boot went all the way down and covered part of the strut housing instead of just stopping at the piston shaft opening ... if that makes any sense.
The more I think about it, I'd think that the piston shaft might be exposed more when it lifts and if the bump stop didn't push down fast enough to cover it. With the 2 piece, it'd always be fully extended and should always cover the piston shaft.