Agree with above comments re explorers and he could also look into a stand alone D of E group.
From experience, explorers (if they also do Dof E) is a better way in that they have more group time and it's cheaper!
University personal statement needs to show some extra curricular activities but anything will do. Its much more about the subject and demonstrating an interest beyond the A level curriculum.
Doing explorers/ d of e should be about the skills they develop ( independence, responsibility, traym work, leadership...) ratherbthan UCAS. My DCs found it more useful for work experience/ placement applications than for UCAS but again these same skills can be developed in any number of ways.
Its also quite possible to pick up Explorers/ D of E after a break if he feels that would be better.
Generally I would say its one if the less important issues so a good one to let them gave free choice with