Never owned the parent .280 but have an AI in a Cooper. Very impressive performance in the Coopers 26 inch barrel. But then, in a 26 inch barrel, most any 30-06 based cartridge can be pretty impressive. I'm a 7mm guy and never saw any reason to consider owning a .270. There's nothing a .270 is ever going to do that one of the 7mm won't do as well or better. If you're a reloader, the .280 has all kinds of promise, particularly if loaded to .270 pressures, and more options in bullets than the .270.
As I said, I'm a 7mm guy and have owned rifles in 7x57, 7x64 (basically identical to the .280), 7mm Rem and Weatherby mag, and 7mm STW. They're all great. Buy a .280 if you like. As noted above, you're unlikely to find .280 in every ma and pa corner store like you would .270s but half the fun of owning things is not having something out of the ordinary.
By the way, if you really want a pleasant to shoot 7mm that'll hold its own against anything but large bears, buy a 7x57. Of all my 7mms, its my favorite to shoot.