This is how it should be done on older solid walled brick built buildings. The damp proof cream needs to be injected in the lime mortar (NOT the brick) and it should be injected every half brick. The hole should then be plugged so that water cannot get into the holes from above (otherwise water will be trapped above the damp proof layer and that sort of defeats the point!) So many older buildings have their bricks injected and this is just plain wrong.
Different manufacturers have different quality products. We recommend (and stock) Dryzone as they have the most silicone in their cream, so they might be more expensive, but having tried some cheaper alternatives (being a cheap-skate myself) I found these not to work, so in fact I wasted my money. If a job is worth doing it is worth doing well. A lesson learned.
Ideally your home should not need damp proofing if you preserve its breathable nature i.e. repoint using lime mortar and if paint use a breathable paint like earthborn silicate paint, Auro’s Lime Paint or a limewash. However, sometimes building societies insist on a treatment that they understand and also damp can be so bad that you need to stop anymore water from getting into the wall in order to give other treatments a fighting chance.
Note that it is almost impossible to inject a damp proof course into stone built / rubble fill walls. For this you will need to investigate using an Electro-Osmosis system to ionically repel water molecules. Sounds fun doesn’t it!