While the new iX1500 comes with a license for 5 computers, if you are upgrading to ScanSnap Home for your iX500 you only get a single computer license. If you normally connect your iX500 to different systems (say use it at home and at work on different computers or move between different computers) you will no longer be able to do that. I expect this also means you won’t be able to use it as a shared scanner over the network, but I’ve no experience with that.
Note that I found the older ScanSnap Manager still works fine (without slow down) on Mojave 10.14.1.