Harris make brushes as good as the best - like all brush makers they have various ranges. I agree getting the best brush you can, is the best thing you can do to start. The rest of the video looks like the actor is working hard to not cut in neatly. Masking tape tends to leave an awful rough edge to the paint as paint will tend to migrate by capillary action under it. Masking tape is not the product - if you must use tape - there’s a special tape for this (I forget the name I’m afraid) but it is NOT masking tape ask at professional decorator suppliers. Secondly when you come up to a socket or light fitting or something screwed to the wall - you will never get a neat line painting up to it - because the surface tension in the paint will always lead to a slightly rolled edge to the paint film (the paint film has thickness) so you must loosen the fittings so the paint under sails the edge. Also - when you later have to remove the light fitting etc - you don’t want the paint to crack round it. The paint nearly always needs to be thinned so it is slightly runny - don’t put too much on but it’s thinness makes it thin out to give a good surface. If you don’t (as demonstrated here with the roller) it goes on like porridge and you’ll get a terrible texture (as you can see in the video) and hairs will be pulled out of the roller. If the paint is too thick you can’t cut a line precisely. There’s a reason that ball point pens don’t have ink the thickness of the paint used in the video - you couldn’t write in neat lines with them. Lastly - when holding the brush - don’t wield it like a club as the actor does - you’ll have so little control. You hold it more like a writing pen, your finger down the stock. If your finger is near “the action end” in Acura use in your movement are not amplified by being away for the line of paint application. Lastly - position your body for stability - and preferably brace yourself eg with your elbow on the wall or wrist if curing in extremely finely .(Eg to sub multimeter precision) as with all tools you have to support the forces with as small a path between the tool end and where your body touches the solid surfaces. Standing back means you are like a tall wobbly crane that will be almost impossible to control. Sign writers use a stick they put on the surface they lean on like a monopod for this reason. Good brushes - but sadly how they demonstrate here will not lead to good cutting in.

U cu

That is not how you cut in at all

That's terrible advise.