No, not quite. It is setup to allow b/g/n connections, but if anyone connects with a b or g adapter, it will slow the entire network to b or g speeds. If only n clients are connected, you should get n speeds. Basically with most basic routers, the connection is only as fast as the slowest client.
That said, just because it's rated @ n 150mbps or 300mbps, it doesn't mean you will get those speeds. Those are theoretical and usually only possible in a test setting. Even then wifi is half-duplex, so you only get max 75mbps each direction with n150, or 150mbps with n300, in ideal situations.
This FAQ should help clear things up. With two clients using the wireless network simultaneously, most basic n routers will give 37.5mbps to 75mbps to each client. It's confusing I know, and the speed ratings are nothing like wired connections which are full duplex.
There is no major difference between the two that I can tell, at least not in any meaningful way for your situation. I would recommend the
Asus RT-N12 D1 over either of those, to be honest.