I brought Harbor Freight AB few months ago because I couldn't wait while my Iwata AB was being repaired at the factory for couple of weeks. It was only $20. At first I hated it because it not as good as Iwata but after few practice rounds I got better handle of it and it wasn't bad at all. Its trigger is pretty tricky...
For sure HF AB doesn't paint very fine lines as well as my Iwata AB does as I have tried several times. I would use HF AB for base coating or primer because it was easier to clean than Iwata in my opinion. I noticed with HF AB if I take my finger off the trigger too quickly, it would spit paint... so you have to be careful with that and point the AB away from the model before you take your finger off the trigger.
I consider it a good back up AB if you can't afford another $150 AB.