The Chamberlain C870 is the exact same machine as the B970, except it is driven by a chain instead of a belt. If you have a big, heavy door this may be a better choice. Belt drive openers all have a self tension spring that can be fully compressed when lifting a really heavy door, causing the belt to go slack for a moment, then “slap” the rail. This problem does not exist on chain drive opener.
It should be noted that the C870 and other chain openers powered by a D/C motor are pretty darn quiet, especially compared to rough A/C motor chain openers from the past. Still, if you want the quietest possible unit, you should consider a belt drive.
If you are looking for a less expensive but still reliable chain drive opener, consider the Chamberlain C450 or C410.