Map activation limits

I'm looking to purchase Ordinance Survey maps for the UK which TwoNav state have three activations.  For me, two will be used for Land and my GPS device, with a third reserved for my phone.  However, if I wish to upgrade my GPS device in the future (something I'm considering), is the map licence transferable from the old device to the new?  Or is there another (reasonably priced) way to move a licence onto the new device without having to purchase an entirely new 3-licence package (which I won't need all of).  Or is the best answer to wait til I have a new device before purchasing the maps I require (which is not ideal either).

Many thanks