If you were using a vfd in order to control the speed of the escalator, a lot of vfds have intelligence built in, so you could just wire it up and have the vfd take care of everything. On the other hand, I can see a bunch of reasons why a current might work really well for a short term demo and start to fail immediately after. Start to get things gummed up or also trying to deal with very small people riding the escalator, the trigger point might be difficult to keep straight.