Yep, all high back boosters (even without head wings) are ~70% safer in side impacts than backless: however, the deep head wings filled with energy absorbing foam do contain the head better & often help kids more reliably remember to stay properly positioned.
If you have the $ to replace the seat, I would suggest looking into the
Britax Parkway or Fisher Price Safe Voyage Deluxe
booster (both have low prices now),
Compass B510,
Recaro Vivo or
Graco Airbooster....
Britax makes the FPSVD & performs side impact crash testing as does
Recaro &
Compass.
Graco doesn't, but their Airbooster design is so similar that it stands to reason it would perform very well in side impacts. FPSVD & Airbooster can be used backless if necessary for travel & the B510 folds for travel.
You can always keep kiddo's current seat as a spare
booster for friends
