Promising this to their fathers seems a bit odd.
Yes, it does seem odd from a catholic perspective. However, all protestants have is the natural law - no Church, no true persons of authority (except in the family). So, the only way for protestants to "legitimize" this "vow" is through the family, hence the father is involved. If catholics did this sort of thing, we'd have a similar ceremony but we'd promise to the priest, in front of the altar (i.e. to God).
From a spiritual perspective, the protestants are just trying to kick back against the ruthlessly impure culture. You don't see novus ordo catholics doing anything REMOTELY like this. I think this takes a spiritual promise to God (which Protestants realize exists) and ADDS a human element, which makes the promise more real (in a human sense). I think it's a great idea, even if it's not catholic. Surely this is a good way to promote purity, even if it's not the catholic way.