Apparently Electro-Hygiene was using the Westinghouse Porta-Vac as one of their "leader vacs" at the time this ad was printed. When I was selling Electro-Hygiene in the 70's, the leader vac was what got you in the house. An ad would be place in the local paper (usually in the classifieds) offering a machine at a rediculously low price. The prospective customer would schedule an appointment and you would go out and show them the leader vac, hoping they WOULDN'T like it. If they didn't, you would tell them "let me see what else I've got in the car," bring in the Electro-Hygiene, and start your demo.
If they did buy the leader vac (which unfortunately happened too often when I was selling), Plan B was to tell them (preferrably before you wrote up the sale) you'd like to show them what could upgrade to later when they were ready for something more powerful. You then brought in the Electro-Hygiene and started your demo and emphasized comparisons between it and the leader vac. The hopeful end result was that they would buy the Electro-Hygiene.
This may sound similar to bait & switch, but the main differences were that we DID have the advertised machines, they WERE for sale, and no claims were made in the ad that weren't true. By the time I was selling Electro-Hygiene the Porta-Vac was long gone. The leader vac we used was called Rex and was made specifically for use as a leader vac. It was a "tin can" tank, cheaply made, not very powerful, and had cheap plastic attachments. The upright leader vac was a Regina Brush-N-Beat.
Jeff