Not a fan of cake safe, at least for the types of cakes I do. CS boxes are not going to work for many of my cakes, and the ones it would work with...even if I wanted to fully assemble them, take the photo with my backdrop, then remove and carefully pack the top piece separately and reassemble at the venue, it seems extremely inefficient. And in my experience the safest place for a delicate handmade cake topper to ride is on the cake, so I don't want anything to interfere with that.
My cakes are staked onto the board either from the bottom up or top down. Proper stacking and staking is more than adequate and I've never had any issues with a cake during delivery. In my opinion, CS is overkill for anything four tiers and under.
If I had lots of drivers going out with a bunch of cakes every week, that might be another story. I might look into it, but I'd also have to train them on finishing the cake at the venue. As it is now it's just me and 3 other drivers who I trust to drive properly.
When I see all the posts here about cakes sliding and falling over, it just boggles my mind. This can only be improper stacking and driving. If you drive correctly, it's extremely unlikely you'd ever have to slam on the brakes. Otherwise 18 wheelers would be hitting people from behind constantly. They can't stop fast either.