no, not replacing... they are two very different boosters... two prices.
the vivo has a shorter seat pan (great for vehicle seats that are also shorter as boosters can't always overlap and fabulous for kids with short femurs (thighs)), the headwings are actually somehow more ample (they stick out further) and I think a safer bet for the sleepiest and floppiest necks... and less body support (actually a good thing for kids with wide shoulders, like my son, Jeffrey, in the long run... he fit the Vivo till he outgrew it... wouldn't be that way with the parkway... and it costs about 99.99 at most retailers.
The probooster has a deeper seat pan (Ruthie's legs JUST bend at the edge... she is not leggy AT ALL), more ample body supports (which Ruthie has declared make her all gray probooster safer and her favorite above her pink &gray vivo... so it's not anything else making her love it), and the headrests are shaped differently (more angled toward the head instead of being super deep... which Ruthie likes as she can see more easily out of the van (in her dad's car, it hardly matters... 2-door car and tall front seats... she's not gonna see much)
neither can be used backless, both have features to make them fit different vehicle seat shapes, but because the Probooster is wider at the top than the bottom, it can be tippy in some vehicles' certain seating positions.
The probooster has more open guides for the lapbelt, though, making it easier in some vehicles to buckle (in my van, it's noticeable, in my dh's car, the belts are of a thinner style and smoother... so both are equally easy)
Both go to about 20-21" in height with the probooster a bit taller.
here are pics of the two