Not sure if my pannier liner is a Bestem or what. I use to have a pair, but one was in the LH pannier box when it departed the ST. This resulted in me only having a RH liner, which I now use in the LH pannier. Not sure about packing 'em so tight that some one, even a slip of a lass like Navgirl, needs to sit / jump on it to close it.
After the pannier departure episode the panniersnow generally stay on the ST, getting them on and off I find a bit tiresome. And worrying, because I now have to check 'em, and check 'em again each time I put 'em back on. Even then, riding down the road I think, "Have I checked?", so I stop and then do another check.
Yes, tiresome. I'm told it will get better with age.