It worked with Richarlison. Also, Rafael who we signed as a teenager worked better than South Americans we bought from Portugal or Europe in general.
edit: Also Martinelli at Arsenal. You get them at cheaper when they are teens, and can adapt them while they play reserves or youth.
Cheaper yes, but they need to play consistently to develop. It's why Chelsea got so much flack the past 10 years of buying players and just loaning them out and they never saw the first team. It's changed a little bit, especially with the influx of technical and talented British youth/younger players and their transfer ban.
Richarlison is still developing, came from Watford and went to Everton with Silva. Everton aren't a top 6 team, especially from the past five seasons where they've finished between 11th and 8th.
Rafa and Fabio are a good shout, but even then, they officially signed with United early 2007 and couldn't make their first appearances for the club until a year and half later due to age limitations.
United have signed some teenagers from other European clubs in the past few years for multi-million pound deals and are developing them in the youth sides, which is best. But allowing players such as VVD, Maguire, etc. play week in week out in their early 20s at lower/mid-table clubs is totally fine. It's part of their progression and shelling out a lot of money is fine when they are established and you know what their consistent floor is (i.e. AWB).