With the dongle, you only can use 1 PC/MAC/Lin at a time - or you buy 2 dongles.
Personally, I use the Key-Version, as this will not block a USB-Port (and dongles can get lost, go defect, eaten or chewed by your usual 2 or 4 legged houshold staff members etc.).
I got my version 17 with a key in a special bundle with a speed editor, switched my M1 to M1Max (and it still seams to work on both devices at the same time... apparently ;) ). hope that helps - br.