Forward clickie means that as you press the button inward, the light comes on. If you let go at that point, the light turns off, so you can use the button as a momentary switch. If you press the button all the way in until it clicks, then it stays on until you click it again.
Reverse clickie means you press the button all the way down until it clicks, and then as you let it back out, the light comes on and stays on. That means it's harder to activate the light by accident (press against something in your pocket) but it also means you don't have momentary operation.
A 1AA tactical light is sort of a weird concept. In a high stress situation where you're illuminating something while aiming a handgun at it, you probably don't care even slightly about either runtime or about battery cost per hour, so tactical lights usually use CR123A's which are expensive but which have much more power density than AA's. Also, it's only been very recently (due to LED technology advances in literally the past year or so) that 1AA lights have been able to put out as many lumens as traditional 2x123-powered lights since the 1AA lights necessarily use a lot less power.
Basically, there are many 1AA lights that are absolutely wonderful as general purpose or EDC lights, but if you're serious about tactical applications, you probably want a 123-powered light, of which Surefire is still the premier brand.