flexfax: why to use class2?

[marco <info@tucsoft.com>]

rh6.1, diamond supra express, hylafax-4_0pl2-3rh5_i386.rpm

I was not able to get fax with rockwell class2 configuration so I tried
with using class 1 and it worked at once.
-I use the modem ( and the line ) exclusively for sending and receiving fax
-I do not want to attach files 
-I want to be compatible as much as possible with other faxmachine
(especially for incoming)

Do I have any reason to struggle with class 2 configuration?

thanks

marco