The Turbobooster is a perfectly decent, safe seat, that will last a long time, is lightweight, and converts to a backless.
The Vivo is really nice too. It's a bit cushier than the Graco (more padding, more comfortable) and it adjusts taller so it will not be outgrown as quickly. However, it doesn't convert to a backless if that's an important feature.
Backlesses are not safer than High backs. In fact in many situations a high back is the preferred seat.
If the child's ears are above the seatback in a backless (common in older cars) you MUST use a high back. For younger children, the back is crucial to keep them from leaning out of position.
High back boosters are now doing a lot more than they used to. They provide substantial side impact protection. Deep headwings lined with EPS foam will protect the head and neck in a side impact collision. As a general rule, you want to use the high back until the kid is too tall for it. Most kids are mature enough to sit in a backless full time around 8 years old roughly.
Naomia might be thinking of the recent IIHS study listing 'best bets' and seats to avoid? Those seats actually tested FIT not safety in a crash. They basically said things techs have been saying for years. Dedicated boosters make an excellent fit and combination seats make a horrible fit. (And most Dorel and Evenflo boosters are unholy nightmares)
Of course, they were testing a 6 year old 60 pound dummy. If your booster got a poor rating in the IIHS study but fits YOUR kid safely, the study is irrelevant.
Julie, my kid rides in a Graco TB on the school bus, it's a fine seat
. The Lizards in Line print at Kmart is adorable *whistles*