I've heard good things about .498 air hammers in general. Downside is the poor selection of the bigger-diameter chisels/bits.
MOST .401 air hammers sold are a pathetic joke. Some--not usually the best-sellers--are quite good. I think that in general, the quality and power of consumer-grade air hammers has come a long way in the last couple decades--moreso than air ratchets; about the same as air impact wrenches in terms of power available then vs. now. That is, you can still buy garbage at low prices, but the mid- and upper-range consumer tools stand a chance at being worthwhile; and even the "pro" grade stuff is improved.
The common .401s are "burp guns"; lots of noise, lots of blows-per-minute, but they don't hit very hard. Pretty-much worthless except for ripping rusty sheet-metal including exhaust pipe. The better guns have ~2/3 the blows-per minute but longer stroke and harder hit.
I bought a .401 CP 7150 so long ago that it's colored black instead of red. Perhaps 25-ish years ago. Does what I need, but I have high-flow couplers and the ability to jack-up the air pressure so the tool actually has 90 psi at the input, with the tool running. Most homeowners have 120 psi in the tank which quickly bleeds down to 100 psi or less, and restrictive hose and couplers--which leads to 60--80 psi at the tool and disappointing results with any and all air tools.