iButton 2 Excel was designed for people who just want to efficiently download data from their iButton device. Missioning needs to be handled using other software.
iButton 2 Excel Full gives the power to efficiently download data as well as automatically mission them for the next set of experiments.
The custom version allows you, the customer, to specify a custom user interface for configuring iButton recording. Maybe you want a custom tag naming convention or some other specific way of setting your iButtons up.