How future safe is this?
About as future safe as anything in the networking world. The IEEE publishes open standards and ostensibly vendors and manufactures adhere to them but in reality you will find that backwards compatibility (and just good old standards adherence) is hard to guarantee in present let alone the future.
A Good Vendor (TM) will ensure that their equipment is backwards compatible with existing standards. If it isn't they should offer you an upgrade of your network switch with some kind of discount (at least in my opinion). The upside of this is "in-place" standards will be around for along time so even after a newer version of that standard is released you can expect newer equipment to generally support it and the older version (i.e., don't expect to see 802.1af go anywhere anytime soon - there are far too many existing devices that use it).
You should contact NetGear and ask what their plans are for the future support of 802.1at (PoE+) with this model of switch is. Since 802.1at (PoE+) is the newest implementation of PoE if you want to be the "safest" with regard to forward planning and have the most flexibility with which PoE-enabled devices you can choose in the future, pick a switch that supports both standards.