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I've had the Yamaha panniers from new (Oct 08) and they've been pretty good really, so much so I've kept them (even though I could do with a bit more space than the 29L they have) - can't justify replacing them as they still work perfectly well and do their job.
Some owners complained about stiff locks and broken keys. The keys have now changed in that they are much shorter to reduce stress fracturing. I reckon that the locks when new just needed a gentle touch (bedding in) - I never had a problem. They are free and easy now after 4+ years of use.
The only thing that has gone wrong with them is that one hinge pin fell out - there's two on each lid so no danger of loosing the lid. I replaced it myself with a bit of stainless rod.
I've fallen over twice with them on (low speed) and no damage, other than minor scuffs. In a hard fall they might tend to bend inward at the back, but the way they are mounted is kind of semi-rigid, so there is a bit of flexing which helps.
Big advantage is that it is possible to attach and remove the boxes without opening the lid, or delving inside to find knobs and wheels! They also leave the bike uncluttered when not fitted (just remove the rubbers or you'll loose them). They are also relatively light - both boxes, the rail and bottom mounts come in at under 10Kg altogether.
They have been 100% leak free.
Would I buy them again though? Probably not, but that's only because they aren't quite big enough for my needs (I'm getting old and like my creature comforts too much when camping these days!). They were pretty much all that was on offer at the time in 2008 and the dealer made me an offer I'd be silly to have refused.
If 58L is enough space for you and they're a good price - get them.