Most are limited to Hodgkin-Huxley currents and simple synaptic conductances. All have built-in restrictions on the number of students they can reach. Most are linked to only one text. All are limited to one or two platforms. A teacher or student outside of the development team cannot modify a model or create a new one.
None has any use outside of the context of the specific exercises that came with it.
The exercises we are developing have none of these limitations. ERL Memo No. ERL-M520, Electronics Research Laboratory, Berkeley, CA, University of California, May, 1975.