Any 16″ bike from a reputable maker with alloy brake levers (standard mark of quality), will be fine. Aluminium frames are a plus, but not a requirement. Years ago, we bought a Raleigh Kobo 16. Steel, but nicely made. Added guards and a bell, and my five yo would easily ride the four miles to school, a couple of days a week. It’s still in service with a neighbor. You can probably pick one up for about £30.
I’ve said it before, but i’d avoid 14″ wheels. Not enough growing time – most manufacturers manage perfectly well with 4″ jumps from 12″.
EDIT: That Blowfish looks a fine bike for the money.