I’ll have a look in the morning, fitted all our shopping in lol and a couple of our foster boys had great fun wheeling it to the car think they will stack ok just not sure on the lock option
On the front left of the photo, it looks like there is a padlock hole in the lid.
It also looks like they are designed to stack, both empty (inside another) and when full - if you look at the lid, it's got 4 grooves which I think will align with the feet of the tub to stack full units.