Many feel that soft panniers are best for off road for several reasons. Having banged up aluminum panniers many times I now tend to agree. You can mostly unbend and re weld/braze aluminum panniers. They will not be waterproof (if they ever were) when you are finished. Field repairs are sometimes a pain.
If the BMW vario plastic panniers hit something (or if something hits them) hard enough they will shatter. BTDT when one fell off of my bike and got hit by traffic.
If I were looking to add panniers to my bike today I'd probably be looking at the Mosko Moto/BMW Atacama bags. The down side compared to the metal panniers I now have is that it would be harder to overload the bike by strapping things on top of the bags. That may be a good thing.