I just bought that also (Xils-4) - it was my first synth at college. I wore that thing out working on it every day! (Never owned one, but have the next best – or really, better – thing now!)
Xils does support the software “soft”-iLok now, though. You do not need a key for that.
Ones that do require a key that I own are those by Lexicon, iZotope, and Exponential Audio.
Most permit the computer-based authorizations now, for which one only needs a free iLok account. That is pseudo-portable in that you can remove an authorization from a machine (you need to do that from that machine) and add it to a different computer. The key makes them all completely portable.
Terry