What are you getting out of this agreement? They already can't stop you from using a word descriptively. They can sue you and lose, but they can also do that after you sign the agreement, on exactly the same theory they'd use anyway ("this use isn't descriptive").

Also:

The product name "secure egress gateway" is obviously a descriptive use of the word (it's a gateway for egress traffic), and therefore cannot violate a trademark. Are they asking you to avoid non-descriptive use of the word ("for your email security needs, contact Egress Software Technologies!"), or are they asking you to avoid using the word in product names regardless of whether the use is descriptive?