I actually have two of these stocks here.
I USE to love the Prime crane stock.
But now... I love the G&P crane stock way much more. It's more realistic, the manufacturing and finish is nicer... overall, I'd say it's a sweet piece on my SPR mk12 mod 1.
ALSO... the battery solution that G&P came up with is much more elegant. As far as I know, it's the only solution out there that lets you COMPLETELY collapse your stock (not that you play it that way, but it matters to some ppl.)