That's a fine idea. Not hard to replicate or use. A DIY'er can see, only the adjustments for thickness/ width of mortar bed [and volume of box] as minor issues. The demonstration lacks how they get a wet edge and finish joints; sufficient mortar is a requirement.
Attachment 25890
Masonry joints deteriorate, especially those which retain a moisture deposit. It's obvious how it occurs in raked or struck, despite tool provides smooth mortar. Flush joints are quick, but remaining surface is porous.
Would enjoy cinderblock fence after connecting single apartment with building. Gauge Hall, as it may become known, will deserve a secure perimeter. Delivering mortar as the GIF shows gets project [linear 250' 76m] back in DIY realm.