Hi Mike
I have used both types of street version and they are great
panniers.I have used the "ordinary street version" with the exhaust cut out and the set that works with the wudu exhaust lowering system both fine .They may not be as stable as the set with the standard tubular steel mounting system,but they are fine for normal touring.These clip onto the normal BMW pannier rail,and it would be difficult for them to come off,I used locktite on the wee nuts that hold them in place and they never moved an inch.They are also locked to the pannier rails.
I have not used them off road,but dont see a problem,the only problem that i could envisage is that they are not secured on the tublar steel rail the full way round the box if you know what i mean,that leaves them a bit flimsy at the rear corner.
I toured with them for three weeks ,with no problem.If you were to be travellin off road i dont think it would be a big deal to Bolster the BM pannier rail and insert a support at the rear.
I have attached pictures of both systems,if you need more clarification ,,just ask !.
By the way Both these systems are for sale.
You can just see the exhaust cut out on the left.