Pressure test kit is a bit OTT for home DIY leaks - the drop in pressure tells you there is a leak but Mk1 eyeball is still required to determine where it is. I’ve never had much of a problem determining if coolant is leaking and where, and waiting for everything to cool down is not that much of chore - good excuse for an extended tea break! Besides which, the system needs refilling properly with engine running to ensure no air locks, some heat through the heater matrix is a good sign that there is coolant actually flowing through there and will test the O rings with heat as well as pressure.
If you can see the source of the leak then its not needed as you say. However if you have one of those pesky leaks that you can't quite locate (for example one that only leaks some of the time) the pressure helps not so much by the loss of pressure, but more by visible leakage that you can get hands around without having boiling coolant dripping onto them when your searching for the source. Most of the time its not needed I agree, but they are a useful tool. The set I brought was similar to the one linked, but was nowhere near as expensive as that one (and they all seem to be that sort of price upwards now).
I think someone on here (possibly Morat?) might have butchered an expansion tank cap and fitted a valve to it to do the same sort of thing.
I've found 20psi is usually more than enough to show up the stubborn to locate leaks, after all the cooling system shouldn't hold a great deal of pressure in any case (and removing the expansion tank cap obviously removes the pressure relief valve)
Duct tape does also vary greatly in quality, the cheap stuff from screwfix is fairly hopeless.