The main idea is the brochure and the friendly, funny and interesting way to present the information about the ISR G2. I use familiar story and several jokes. Style is restrained as the target group are companies and company managers.
My personal opinion is that the letter is the best way to send your message directly to the target group that in this case is small. Advantage in the case is the low cost of the letter compared to any other kind of advertisement. Also the letter is image making as this shows your direct interest in working with specific company - especially if the brochure is addressed and brings the feeling for special attention from "cisco".