Hmmm. Underrated? Well, perhaps. My own opinion is that they are IN GENERAL (dangerous words, those) good to very good, but not fine or excellent, products. I've come across good and bad examples, which of course also applies to Pietta, Uberti and even Colt's Manufacturing Company, Inc. To the extent that there's a popular bias against ASM guns that alleges poor quality, then yes, I'd say they are underrated. However, I'm not really sure that the popular opinion is all that bad. Lots of people like them.
There are brands of bp guns that I will not lift a finger to investigate for purchase. ASM is not one of those.