Except it's not 975RP. It's a skin (and possibly Sona) free. Assuming you don't own all the champions you'd probably be able to buy more than 1 single champion once your 20 wins are over. If you do have all the champs then there's runes and shit. If you own all those? Well, sucks. But there was also 1% of the Korean population that already has Silent Night Sona, so sucks for them too.
I'd much rather have a 20 win RP boost than have a skin basically equated to Riot Girl Tristana/Golden Alistar levels. Then again, Arcade Sona is best Sona.