I own several. I would say they are almost on par with Benchmade, or Spyderco, meaning a very good production knife, but not perfect. They have some very good designs. The fit and finish can be lacking sometimes- I have had to sand the G-10 to be flush with the liners on a couple, and the blades are not perfectly centered on a couple, but functional. Their S30V is quite good, and holds an edge very well. Every knife I have received has been very sharp. D/A scale release is very good. The Paul series is an excellent gentleman's knife, but a bit finicky. Don't get any dirt near that axis release button, the tolerances are too tight to handle the grit. I wish they used better steel for the smaller Paul stuff, but it is not meant to be a hard use knife. They are bit pricey, but about in line with comparable stuff. Their customer service is great. Here is a brief run down of my thoughts:
Paul executive carbon fiber- excellent fit and finish. Great axial lock. budget steel. My favorite dress up knife.
Paul Presto- great fit and finish, but the locking mechanism was not right. Warranty service was superb- they made it right and had it back to me within a week. Fun, useful light duty pocket knife. I wish it was S30V or 154CM.
Diablo D/A- super fit and finish. Above average liner lock, superb scale release. Love the S30V, and the blade shape. The FRN scales feel a bit cheap, but I love the knife. It gets babied, but fun to carry and scary sharp.
Harsey T1/T2- The T2 fits my hand perfectly. A very hard working knife. Locks up solid, and has the S30V. Lock up is rock solid. Pocket clip is the only weak point, as I think it rides too high. The T1 had scale fit issues, and the thumb stud was a bit sharp. Both knives blades a bit off center. I love the Harsey stuff. Very useful design.
I am not too familiar with the newer designs, but they seem to get good reviews. I recommend trying one. These guys deserve some support, considering their good customer service and the fact that they are domestic. Call them up and see how they treat you.