I used them on my trip around Asia and am really convinced. Had a few bad falls and they are still waterproof. Met a guy on an Africa Twin who told me that he hit a rock at 50 kph. His box sure looked like that and it was supposedly still water proof.
Also, no hinges (take off the lids without unstrapping your soft bags) and they are not as wide as the handlebar, so I do not have to think about them when riding.
Only for me, 49l per box are too much. Its not only the space, somehow they are always full with unnecessary stuff. I heard Tesch is now offering 35l boxes. If that is the case, I would get them instead.
Also, I would really recommend building a quick release system. The boxes are very handy as chair/table, when the bike fell or got stuck or when doors are just a tiny bit too wide etc.
Here is how my quick release system looks like
Quick-Release
The boxes got further modified (handles, padlocks, different bolts). Have a look at the pictures on my web site.
One more thing: Build your own rack. The tesch one is just too heavy hand and had to be bended (not easy!) to eventually mount it successfully.
Lars