I think it comes down to scaling issue. I do believe they make excellent entry level PCPs due to their price; however, there are pros and cons to that. In general, people like getting deals, and AEAs appear to have excellent value when it comes to cost respective to their quality (or lack there of). So here's what I think is happening. Less people, especially beginners, purchase PCPs with similar features that cost north of $1000. If 1 out of 100 is a lemon, then we only hear one person complaining about it. If AEA sells 1000 with the same lemon percentage, you have 10 people complaining about it. The fact is a lot of people buy AEAs. I know a handful of people who have really nice FXs and other premium PCPs that still purchase AEAs as plinker/truck guns.
Unfortunately, the quality control is also impacted by the number of air rifles/pistols they churn out. That's just statistical reality. That being said, your odds of getting a lemon out the gate are higher than going the "buy nice, or buy twice" or " buy once, cry once" route.
Peace of mind in itself has value, so I typically recommend just getting the dream gun. Sure, it's more than you'd ever thought you'd spend, but every little detail just adds up in the end resulting in a more enjoyable experience. Your odds of getting a lemon are smaller and, if you do have issues, the customer support is usually better.
Personally, I own two AEAs, and my first one, HP SS Plus 30 cal, had a leak at the gauge when I got it. I just tightened it a degree to fix it. Then I had to learn how to make it run properly. The semi-autos like perfect pellets / slugs. eBay pellets with casting flash and Hatsan Vortex don't cycle well. I've found that it shoots NSA slugs 49.5gr and higher accurately and reliably from about 3200 psi for a good 50 shots (I upgraded the cylinder from 300cc to 450cc). The slugs are also quieter. When I say accurately, I mean "Minute of Squirrel's head" at 25 yards. When I say reliably, I haven't had ANY cycling issues. No low powered first shots / short stroking even when filled to 3600 psi. That being said, I only shoot slugs out of that gun now. It is my work horse, and I use it for pest control around the house. It's great for rats at night.
The issue my .357 Challenger has is I need to fiddle with the fill probe before it gets a good seal. I changed out the o-rings, but the issue still remains. I tried one size up, but I couldn't get the probe in at all. There is an in-between size I've just been too lazy to order, because that minute it takes me to find that sweet spot isn't that big of a deal to me. Another annoyance is how loud the action is. I also use NSA slugs out of this one, and the sound out of the muzzle is very quiet. I still run an Emperor moderator on it, but the action will still get nearby birds to fly away when I shoot it.
The AEA groups on facebook are equal parts praise and complaints. That's not good. If you're the kind of guy who can live with interior panel rattling in a new car, the AEA is probably a fine gun for you. If something like that would drive you nuts, look elsewhere.