What is the advantage/disadvantage over a solid pilot and removable pilot? I have always used a solid pilot as they were standard cartridges. I now maybe having to look at a removable one.

One obvious advantage is the ability to match the pilot exactly to the barrel/bore dimensions.

As long as it matches you bore, there is no difference. The removable one, as stated, allows you to make pilots to fit non standard bores. I make them from brass.
I have heard from non users, that solid pilots will scar the bore. More nonsense; they won't.

I know of a gent who removes the pilots from his reamers before chambering/