Subcontractor carpenter here, I work on a lot of different sites and don't leave my tools on site at night, nor in the site container either.
I only have one Festool tool, its likely the same first one as many people get as its the plungesaw.
I actually started to get the Tanos T-Loc boxes
before I bought the plungesaw. Bought a Metabo jigsaw to replace my about knackered Bosch and the Metabo came in a No2 T-Loc box, then I've put my two Hitachi cordless drill and rattle guns in a No3 attic T_loc box. Oh and a De-Walt compact router combi kit in a no 2 box.
The T-Loc boxes for exactly into the floorplan of my
Clarke Sitesafe that's in my van, three lengths of box fits into the one length of sitesafe. Two widths of the T-Loc boxes fits into the width of the safe with just enough space that the French cleat things on the bottom of them fits into the other box below.
Then five T-Loc units (a No4 box and a No1 box or a 2 and a 3) make up just the right height that I can fit my Makita chopsaw into the safe and close the lid one one side and also I can get my nailgun boxes into the safe as well cos they don't fit in T-Loc boxes.
Now I've ratched a few castors out and made myself a wheeled cart for the boxes, that makes getting my tools offsite quicker and simpler and when they are on site they are all on one place.
Plus the little trolley I made for them is handy for moving dead heavy stuff over flat floors.
Those boxes make my working life simpler, tidier and mean I can fit more tools into my toolsafe.
They don't make sense till you have a few of them though. I am sick to the back teeth with the mismatched crap that the other manufacturers put their tools into and nowadays if a tool doesn't come in a T-Loc box it better be the price of one of those boxes cheaper than the one that does or I'm not buying it.
Was never blown away by the old Systainers though as the catches seemed fiddly to me.