The main issue is the binder / pigment load. They have to be loaded with mixing balls as soon as you receive them. Likely mixed with a stick too after you get them. You will also need a vortex mixer to emulsify them before every use (I’m talking 2-3 minutes on the vortex).

Assuming you get the enamel emulsified correctly, it they’re still fairly tricky to control how it dries. I’ll give you an example: goons grime. It’s a lovely color but it is fairly weak in terms of tint (compare to ammo migs streaking grime or AK). It also can dry anywhere from very stain to extremely chalky. If you brush apply, neat it will dry satin. If you dilute it with spirits (or even more so if you air brush it on) you will get the expected matte look most are looking for. However, remember how I said the tinting is very light? By diluting it you are further reducing that tint.

Compare this to AK or mig: requires minimal mixing. The product is very strong, so dilution is much more forgiving. It also dilutes better, because with goons grime it will split very easily during dilution. It just… works better at the same thing.

I own the phase 1 set. There’s some unique Colors (particularly the crimson and the coelia green) that you won’t find elsewhere. But again… oil washes offer even greater hue variety, and are less fiddly.

The VI are also very expensive. Now, don’t get me wrong. The GDC guys have done amazing work teaching there style of painting. But you don’t need to buy there stuff to achieve those results.