Compared to my converted cocker, it's definitely right up there along side it. It's got a very smooth action and it's very comfortable to hold ans use as well. The stock barrel isn't bad at all, but you'll probably get better results with a tighter bore barrel though. And you're right, it comes with standard threads and what not. The feednecks thread is a Ion thread, so you can put any after market feedneck on there and the ASA has the standard screw threads and spacings you'd find on most other markers out there.
But overall, it's definitely a very nice pump gun for the price. My mate managed to import his for around £130 and that included customs tax. I'll definitely be getting on once I've got the spare money!