Yes, mifold is currently legal in the UK and Europe. It's permitted under the older ECE R44/04 standard. Once new R44 seats are no longer allowed and only newer R129-compliant seats are approved, the minimum height for all backless boosters in the UK and Europe will be 125cm (49"). That's the size of an average 7 year old and is in line with both best practice and the size at which mifold realistically starts to fit children safely. Some of the details of R129 "booster cushions" (backless boosters) are still being ironed out but heightless boosters like mifold may eventually need to be redesigned to comply with design specifications.