#1 - KEYWORDS+"of"+MAINKEYWORD.com = a very suitable searchable phrase
#2 - KEYWORDS+MAINKEYWORD.com (same as #1 but without "of")
According to the Wayback machine, #1 was used in 2001 and then again in 2007. It has now expired. It is not currently indexed by Google, but there are references to it in forums where it is associated with an eBay scam. Also the .org version (KEYWORD+KEYWORD+"of"+KEYWORD.org) is a no-content made-for-adverts site which has nothing to do withe domain name.
#2 is not indexed and appears never to have been used.
I don't intend to use #1. But if I were to use #2, as it is so similar to #1, are there any dangers involved?
Also if I were to use #2 it seems sensible to also obtain #1 to prevent it being used in future. But would the WhoIs info associate my other sites with its dodgy past?