Just to resurrect this old thread...
I can confirm that the KA spiral hook works very nicely on a Hobart N50 (I have the K5ASBP bowl, rather than the OEM 'official' ST005).
I accidentally bought the burnished spiral hook, wide bowl (KNS256BDH), rather than the KNS25BDH as Amazon has the part numbers and titles mixed up!
. Stoopidly, they have the spiral hook for the wider bowl (KNS256BDH) listed as a spiral hook, burnished - but the spiral hook for the narrow bowl (KNS25BDH) listed as "burnished spiral, wide bowl" : http://www.amazon.com/KitchenAid-Dough-Hook-Burnished-Spiral/dp/B003DYZW1C/?tag=pizzamaking-20
However, a search for "KNS25BDH" on Amazon shows up BOTH versions (one correctly listed, the other not). Sigh.http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=KNS25BDH&x=0&y=0&tag=pizzamaking-20
So - LET THE AMAZON BUYER BEWARE! Or at least if you want to avoid my fate of ordering the slightly wrong hook!
Anyway, the new (slightly wrong) hook works very, very nicely. Although the stock N50 hook is a well-machined heavy duty item, the KNS26BDH is no slouch either, and looks suitably industrial - well done KA on this! I can't believe how cheaply these are going for.
Performance-wise, there is no more dough climbing, and it seems to give it a good thorough knead. I'm pretty sure the over-engineering of the N50 will minimise any untoward effects of the spiral action on the planetary - but will report back if there are ever any issues in this regard.
The only minor issue is that there is just a fraction too much clearance above the bottom of the bowl, which means it needs a little prod to get the dough to come together with smaller batches. Larger batches (>1kg) are fine, and once the dough is together, the kneading is excellent. As noted above, this is due to having the wide bowl version (which surprisingly has adequate clearance around the bowl).
I've just ordered a KNS25BDH from ebay... this is a slightly deeper / longer hook, so should be perfect. Will report back in due course.
[EDIT: Amazon has just emailed, thanking me for pointing out their error. They fully refunded my purchase AND - due to the return shipping cost - allowed me to keep the KNS256BDH. Great customer service to 'em, I say!]