Ceiling Light Installation: Junction Box or SLIM Led Driver Differences
In both cases a box is required. The advantage today is the slim may be cheaper, but in the future you may be tied to a slim box.  This could become a problem when all the mfg’s are only making replacement modules for full sized boxes because of the millions or hundred of millions of full sized boxes currently in use. How many slim boxes were ever installed?
The other consideration is that if other wires are in the box to connect to other lights, there is a minimum number of cubic inches required to accommodate those wires, so in this case, a larger size may be required today and provides more options when this light fails (LED’s rarely fail but the electronics driving them sure do).