"I will start off with saying this style of gun has always been a favorite of mine, so I am loath to admit any failings, but there are some rather important ones. We can start with those, then move on to why I still give it 4 stars.
Picking up the AUG, first impressions are very good. Fit and finish is typical of JG products and if you expect perfection, spend more money. The only steel on the gun are the sling attachment points, the seams are visible in the polymer body if you're looking for them and nearly every screw can do with some tightening. Push the safety switch too far, it comes out. Play with the mags enough, they will start to wobble. Pull the trigger enough times, it will start to stick. On the plus side, the problem I see reported most with this AUG, the two stage trigger, appears to be an easy fix after a field strip. And learning to field strip this weapon seems to be required. There is a gap in the magwell that leads to the inside of the polymer shell. If BBs are not fed into the gun directly, as most hi-caps leave a few in the queue even when firing dry, some BBs can fall into the inner workings of the rifle. Field strip and shake them out, it's fine, and they don't seem to be able to cause any damage in there, but they are very audible.
The small battery compartment can be considered a con as well, but personally, the high rates of fire that come from 9 and 11 volt batteries are not my personal preference. I find they take away more of the realism when guns fire 1200+ rpm. If battery upgrades are on your list, the AUG will make that difficult.
The biggest problem with this gun is the metal half. The gearbox is fine, powerful but with a torso-sized spread at max range even with .25s, but again, JG expectations. The key problem is in the sight. Whatever metal they built this out of is easily the softest metallic alloy apart from lead. Ten minutes using proper tools and both adjustment screws for the sight were stripped bare. Apply a bit of torque, which is very much needed to push the stiff scope towards zero, the threads actually wear to nothing. My very first modification to this gun has been real steel set screws, but even these bite into the soft metal carving out new threads with every turn. It seems to be the only option considering my crosshair was about 4mm below zero to begin with.
Now the good points of this rifle, and once again, I'm very biased in favor of this rifle considering it was a childhood dream of mine.
The scope's positioning is very ergonomic. Resting your cheek against the gun immediately puts the scope exactly where it needs to be, at just the right distance from the eye. The eye relief is only a few inches, no more than 3" at most, but I haven't had a problem with seeing through it the moment I put my head down. With a full face mask, however, this seems like it would be next to impossible. Even with my Iron Face lower mask, it gets slightly complicated, but soft face protection shouldn't have a problem.
The trigger group is designed amazingly well for right handed shooters. While it is true the gun is ambidextrous, even with a rubber bolt cover that can be switched to either side of the gun, the safety knob gets in the way of 'meatier' hands on the left side. As a right handed shooter, turning off the safety is as easy as holding the grip.
The option of barrel exchange is a big bonus for me. Playing in multiple environments, I will be picking up an extra outer/inner barrel with hop up to convert to a field sniper as well as a shorter barrel assembly for CQB fields. With practice, changing the barrel can take all of twenty seconds. Same goes with upper receivers.
The magazines were an unexpected pleasure. Having learned how to shoot assault rifle on the AK platform, my muscle memory for a reload is very different than one for an M4 user. The AUG uses a button to the rear of the magazine to release the hold, then the magazine is pulled out, but to put one in, the feed portion of the mag protrudes, allowing a very useful guide to slam the mag home. Angles aren't as important as anything but the most extreme of foul ups will push the magazine in. As my first bullpup, and my first non-AK platform, it was very easy to learn how to reload efficiently.
TL:DNR version: If the AUG A1 is what you're after and no one can persuade you otherwise, be prepared for some extra work off the field. If you think the scope is just 'cool', go with the AUG A2 (UA-1 Civilian) or the A3 model. Less hassle with aftermarket optics. The AUG is surprisingly easy to get used to even if you're unfamiliar to bullpups. Aftermarket options are limited unless you get creative but it still serves very well as a back up AEG."