Like Mickey says.. Most people start off with hard boxes as it is copycat ! I did it... Expensive lesson. All the magazines, books, catalogues and loads of people on the hubb seems to tell you to buy them.
But what I found is all the people who told me "YOU MUST HAVE HARD ALU BOXES" had never travelled offroad or even out of western Europe. Of course, thats not true of everyone but you get my point.
It's very hard to guage good advice on the Hubb. It is all very well meant but very difficult to judge opinions. I think (and again just my opinion) that you can only listen to people who have actually been there, done that and got the broken expensive boxes (I mean Tshirt).
I used to recommend my Metal mules to anyone that would listen. That was before I actually really knew what it was like to drag them through sand or gravel roads or to try and bend them back to shape so they would close again. (IMPOSSIBLE)
A great deal of people who have travelled with big heavy metal boxes swear that the first thing they will do when they get the chance, is swap to a lighter, softer luggage system.
I think the biggest consideration is the road conditions. If you're riding tarmac or very easy trails then ANYTHING will work and it's not really a problem.
If you are really considering daring or challenging offroad where there is a high chance of multiple drops and tumbles, then IMO you'd be mad to have anything but the lightest, most flexible and easiest to repair luggage. And that means softbags.
I dont think people really realise just how big, wide, heavy and cumbersome these aluminium boxes are until they fit them, load them and then go for a test ride.. "HOLEY F**K" is the usual response !!
Back to the point.... They are big heavy sharp metal things and they can and do fall on you in tumbles. I was trapped under my bike on the Ruta 40 by mine and I do believe that the only thing that saved a break was my massive Alpinestars Tech 10 boots.
Whatever you do.. BUY BIG PROTECTIVE MX BOOTS if you're offroading at all.