Today was my first time using a jump strap - big warmblood mare, green but willing.
WOW! I loved it! Really made me reach up and made the awkward jumps much smoother to ride. Even though I only actually grabbed it a couple of times, just the mental picture of reaching for it really made a big difference!
Incidentally, I had bought this one per recommendations on here:
http://www.ebay.com/itm/Horse-Jockey-Leather-Neck-Grab-Strap-New-/180853179505?pt=LH_DefaultDomain_0&hash=item2a1bb08471
a while ago, and while nice leather and well made, it is HUGE - I need to punch some extra holes in it. I think it was made for an elephant!!!