It's actually really easy when you know how. I swear! But it can seam a little daunting when you have one pre-2012 bag and one newer one. They are completely compatible (all Kriega gear works with the rest of the range regardless of age), but I will admit we could explain it better. I'm actually working with the Kriega lads back in the UK to put together some instructional videos, which should make everything crystal clear.
The switch was made simply because it's a better system. What we found was that - while our bags could handle pretty much any thing you could throw at them - the same could not be said for all seat mechanisms. With the development of the US-30, people could put a staggering amount of luggage on their bike if they wanted (e.g. a UScombo70 with another US-20 on top = 90 liters of storage, which is a lot). During R&D, Kriega discovered that his kind of bulk, combined with rough roads or extreme acceleration, high speeds etc, created the potential for the rear seat pad to pop its lock on certain bikes (probably not the 675 though, on account of that annoyingly hard to reach, but strong bolt, which holds the seat on).
So to ensure that this didn't happen, a new mounting system has to be designed for the bigger bags, which involved attachment to the subframe (or any appropriately placed, solid mounting point). Hence the Alloy Hook Strap system.
After seeing this in use for over a year on the US-30 and hearing the extremely positive feedback (more secure; easier to remove the bags; leaves no evidence of luggage when the bags are lifted off the bike - i.e. no loose strapping to tidy up or having to remove the seat to get the compression straps fully off the bike; works well on racks etc.) from riders who had this bag and those who had upgraded the straps on their older US-10 or 20, they decided the benefits were too many not to upgrade the entire range.
I'll admit I was a little dubious at first because it put the price of the packs up. But the two chaps who own the company and design all the gear, were positive it was well worth it. They're pretty smart fellas and serious riders, so, I agreed. And as it turns out, we're selling more than ever and getting great feedback. Although it can seem confusing to start with, once you've nailed it the first time, it all makes sense.
I may be biased, but it's for all the reasons: I've been using Kriega tail packs (UScombo40 and US-10 on the tank for long hauls) and backpacks (R25) on sport bikes for over seven years now, but only got involved with the company professionally mid-way through last year. And I still use the same gear I bought back then... (with the upgraded straps on the US packs, of course!).
I'm actually taking a 675R on a 1,200-mile road trip to Pikes Peak in July
, so I'll load that sucker up good and proper and take a bunch detailed photos of the installation and various options for y'all.
Let me know if I can be of any further assistance.