Been reading through the rules on this and it seems to me that a mage could function just fine being in a constant state of Astral Perceiving and basically do alright. I'm imagine certain stimuli like sound and smell would have no effect on a person doing this but they would be almost impossible to sneak up on. So my question simply is how effective would this work? Is astral better than regular perception?

Different? Sure.
Better? Depends on you skills.

Astral Perception is not exactly analagous to any of the five sense you or I have. But it is most analagous to vision. Astral Perception is directional and blocked by intervening objects. If a man can sneak up behind you or hide behind a wall in the physical world, chances are those same techniques work on the astral as well.

Now there are obvious advantages. A mundane disguise is of almost no help against astral perception, but of course it is spirits hard to disseminate photographs of astral auras as well. There are obvious disadvantages as well. Letting loose a cloud of FAB is essentially invisible on the physical plane, but it blocks astral perception as well as a mountain.

-Frank

Physical Drain from being astrally active is the most common reason not to leave it up.

Wasn't that one of the changes made in Fourth?

Sorry, having a bit of them old edition fogies. Back when they were introduced, living forms were inherently impenetrable on the astral - and FAB were simply "extremely alive bacteria". They were gaseous and invisible on the physical, but impenetrable on the astral. There were used as "organic restraints" back in the Corporate Security Handbook - you'd spray them into an area and if there were any astral inruders they were stuck. You could even shine a UV light on them to show you an outline of what you were going after so you could taunt it.

Heck, back in the old days the "F" in FAB stood in for "Fat" rather than "Flourescing" because the salient feature was simply that it was a living entity rather than that it under some circimstances shined.

Sorry, we now return to Fourth edition rules where FAB is a bad example and I would have had to use a low force area spell effect instead.

-Frank