You MAY see increases to an inch. It will not be permenant. I use to sell them for a medical company, trust me....i have 3 different types, they work on the same principle....vacuum.....duh.
I have even used the Jes extender (http://www.jes-extender.dk/cms.ashx) - My boss purchased 2 of them. 1 for development of different products and 1 for someone to use to see if it actually worked. I told him if I was not the one that demo'd it, i was going to quit. He gave it to me free of charge.
What i did not realize, they say it takes 1000+ hours for permanent results...i may of used it for 20 hours. I gave up, but the little shit is cool as hell. Looks painful, but not at all.
As far as the vacuum pump, if you use it for 7 days straight for 5 minutes of maintained vacuum pressure per day (pressure is around 14-16 inches mercury) you may see 1/4" gains TEMPORARY....if you dont use it for a couple of days. The rabbit is going back in the hole.