Good points. You'll see specials on P4A because they don't sell as well, for good reason. They use the same anemic GL300C controller the P4 uses, really poor range. With P4A you'll likely end up spending another $150 on a better directional antenna to improve range, which helps, but you still won't get the 4 mile range that P4P gets on 5.8ghz. You'll see vendors dump P4A craft occasionally with low pricing so they don't sit too long.
Does the P4A really use the exact same GL300C controller? If so, that would mean that you could also use the superior GL300A controller to get 3+ miles out of it, right?