Is stageClix Jack, as opposed to many other systems, legal to use worldwide ?

The chosen frequency, 2.4 GHz band, is available worldwide and therefore legal to use.

Does stageClix Jack cooperate properly with active elements (e.g. active basses) ?

There are some active basses with a poorly shielded active elements, which confilcts with stageClix Jack.
To solve the issue with those basses / guitars - we suggest to use the extension cable which is available by all our dealers in Europe. When you can not find a local dealer nearby, all accessories are also availble at our own webshop.