i think there are only 3 or 4 boosters on the market that don't have a tether strap, most of them do.

i had to go for a slimline one to fit, and i have found the booster the most difficult to work around because the buckle side is next to another no matter where in the car it is positioned. So, if you want booster next to another seat or booster, you want to check accessibility to the buckle.

i have a hi liner in one car and infa secure vario in the other. i prefer the Vario, but my dd is only 4 so i'm not sure which will be better as she grows.