Other manufacturers may not copy because it adds a lot to the cost and a lot to the weight plus there is an art to winding them and Mac has been at it for over 50 yrs.
If you compare the sound quantity (not quality, that's up to you), of an AF Mac with 250 watts to say an older Krell with 125, the Krell will play louder on 2 ohm speakers, the same on 4 ohm, and not as loud on 8 ohms. That was one of Macs selling points: You buy a 250 watt amp, you get a 250 watt amp. Long ago and maybe not to far in the future there were some 16 ohm speakers. Mac used to have 16 ohm taps, (I think their newer 275's still do), the Krell would put out around 63 watts on them. These are only 3db differences. As Horses2harleys noted, if you want to play twice as loud as 125 will give you, you'll need 1250 watts
All the others here have made great points on why AF's are a good thing. My fave is that it allows the output stage to run at its most linear point. Linear is a good thing.
There is no perfect amp. It just doesn't exist. When you hook up any amp to a resistor, it may test very well. Speakers aren't resistors. I like the path that Mac has chose.
If you compare the sound quantity (not quality, that's up to you), of an AF Mac with 250 watts to say an older Krell with 125, the Krell will play louder on 2 ohm speakers, the same on 4 ohm, and not as loud on 8 ohms. That was one of Macs selling points: You buy a 250 watt amp, you get a 250 watt amp. Long ago and maybe not to far in the future there were some 16 ohm speakers. Mac used to have 16 ohm taps, (I think their newer 275's still do), the Krell would put out around 63 watts on them. These are only 3db differences. As Horses2harleys noted, if you want to play twice as loud as 125 will give you, you'll need 1250 watts
All the others here have made great points on why AF's are a good thing. My fave is that it allows the output stage to run at its most linear point. Linear is a good thing.
There is no perfect amp. It just doesn't exist. When you hook up any amp to a resistor, it may test very well. Speakers aren't resistors. I like the path that Mac has chose.