TMS FNC Core / TMS FNC UI Pack are backwards compatible, at source level, not binary unfortunately. When a BPL is compiled, it needs to be recompiled when a dependant BPL is recompiled.
Because we want to offer separate packages. Someone interested in TMS FNC Maps might not necessarily be interested in TMS FNC UI Pack and vice versa, also, TMS FNC Core can be purchased separately. Additionally, when one decides to purchase another FNC product, it can co-exist with the other products, because it uses the same base TMS FNC Core. We are aware of the flaws in the installation process, it's currently unclear what the best approach is but we are investigating several paths.