I just had a Huma regulator installed in a AA Sl400 in 177. It was a pleasure before the regulator but the upgrade and "tune" really helped. I shoot 40 shots at 870FPS and then refill. I should test the shots per fill, but I usually only have enough concentration for 40 shots offhand. I shoot silhouette, and I usually shoot at 38 yards. From the bench I can it a dime every time.
I had an unregulated Regal and it was a pig. I had to send that one back to AOA, and that was a PIA. The Regal in my opinion is too light, and the shot count was poor. Mine had a bad barrel or something because I had 3 inch group at 30 yards with different pellets. Naturally that was a manufacturing error and that happens, but it never felt solid to hold, and that is my taste.
Before I had my AA400 upgraded I was going to get a HW 100, but I was a bit afraid of the reliability based on research or I would have bought one. But it was on my short list.
In the end, I am pretty happy with the 400 bucks (I think that was the cost) of the upgrade. I am thinking of buying a factory regulated AA500 just for the dual gauge, but the cost is pretty high on those. I owned an embarrassing amount of nice airguns, and for the money the AA400/500 is probably my favorite.