After mulling over this for a while, I've decided to share what I've witnessed and experienced (as a guy), and what I've heard from another medical professional.
I had never heard of any kind of vacuum pumping until I had to start taking a hypertension med which introduced me to the terror of ED.
While still confounded by that new development in my life, around the same time I'd read that the FDA had approved a clitoral suction device, available by Rx only, for women with "orgasmic dysfunction"...
Shortly after, I next read about the FDA approving a device for breast enlargement called the Brava system...
My curiosity now piqued, I started doing some research online and discovered that female genital vacuum pumping seemed to be more of a European thing than it is in the US.
Long story, but I later wound up actually having a conversation with an RN who runs a women's pelvic floor heath/GYN practice with her MD husband. She told me she'd never heard of pussy pumping until she and her husband were traveling in Europe and ran across it as an OTC home remedy available from pharmacies for women with orgasmic dysfunction, vaginal dryness, or atrophied vaginas who wanted to resume intercourse. In her opinion, what happened was the general public start using it as a sex toy, then the porn industry took it to extremes, which is what you usually see on websites.
In her opinion, and she confessed being a personal advocate, was that it was actually beneficial to female genitalia to encourage engorgement and circulation, but that massive swelling seen in porn was probably not a good idea and might lead to labial stretching, prolapse, etc. Since the sensations could range from "pleasant" to "uncomfortable" to "painful", her recommendation was to always keep it just under "uncomfortable" and it was best to let the woman do it herself so she could best determine the sensation. Her preferred regimen was 30 secs "just under uncomfortable" followed by 5 secs release, cycling over and over again up to 20 mins total. Swelling would be hardly visible but sensitivity would be markedly enhanced.
In my personal experience, I've pumped a gf using the above regimen and what happened follows. She was initially skeptical but mildly interested and after about 20 minutes, started feeing a bit impatient and bored so we stopped. There was hardly any visible effect and since I had a good erection at the time, I entered her body. I kid you not, her eyes rolled back in her head and she said "What was I thinking?! You can do that to me anytime you want!" We then had an mindblowing fuck and both came in just a few minutes. Her vagina felt very different to me (in a nice way) and obviously she noticed something different herself.
In reading various European sex forums, such as joyclub.de as well as others, swelling only occurs with practice, where the tissues are basically "trained" to become engorged and congested, and it usually takes between 40 to 60 minutes of cycled pumping. (Static pumping for long intervals is a terrible idea since blood will pool and tissue damage will occur.) A tube like a penis pumping cylinder is also a bad idea because it focuses the suction on too small an area and is too deep. A cup designed for pussy pumping is preferable because it distributes the vacuum over a much wider area and is not essentially "bottomless". Long session pumping will eventually start to fill the cup and repeatedly filling it over time will cause the swelling to become more and more permanent. The Euro forums also universally praise a cup from the German company Froehle, which is also the top selling pussy pumping device on both Amazon.uk and Amazon.de.
That is the one I have and have used on some of my girlfriends. I believe it is the best designed and is probably the most comfortable due to its large rubber cushion.