As a comparo, the Seahorse are 26L. They don't overwhelm the back of the bike at all. It looked kind of big on the Versys, hung off the back some. But fits the Tiger perfectly.
They are the same as Storm i2400 or Pelican 1520.
Carribou cases makes some nice stuff, but for me they are rather large and rather expensive. I enjoyed coming up with my own installation for half the cost.
My top box is bolted on, not removable. I don't bother locking it, but I don't leave the bike unattended in public places. I guess I really need to pick up a padlock set for them should I ever need to lock them. Same deal here, Carribou has nice cylinder lock sets for their cases, and quick-disco hardware. That's where the extra cost comes in.