I tried such a cup here:

http://www.youtube.com/watch?v=PDPvc8Vhz1c

It has a hole on the top which you can put your finger on to create a vacuum but I wasn't really sure if you should only cover it when you pull out for a sucking effect or also when you push it but when you also cover it when you push it in then where is the air which is in there supposed to go? Could this be dangerous if the air cannot escape and then it is pressed into your urethra? Do you think this could be sold if it was dangerous? I only tried the vaccum a few strokes and then stopped it because I thought it might not be safe.
First I tried it without condom and it didn't really feel that great. If a real vagina feels similar to this then I would be very disappointed. It was also pretty hard to insert my penis in it which is kinda weird cause I'm not that big.
And after cumming the first time I directly tried it again and put on a condom and then also applied some extra lube because this thing becomes dry pretty fast and then I banged it and after a while the condom burst! I really hadn't expected that a condom could burst in there because this thing is pretty soft in there and then I went on without condom for probably 20 minutes or longer until I finally came a second time but the orgasm wasn't very good and I also did not feel much. Overall it's not really that good and I had expected more. The only thing it was good for was to get an impression how it must be to hump a vagina and I was also able to try different movements for example I held this thing with both hands on hip level and then went in and out in a straight line or then held it a little higher or lower to simulate different positions or another thing I tried was instead of only going in and out doing a circular motion and moving it in and out while at the same time moving the hips from side to side to get a bit of an angle. Do you think chicks would enjoy such a motion?

Anyway what do you think? Have you ever tried such a thing? Do you also think it could be dangerous if you get air in the urethra? I think the cup is made for 1 time use but I'm gonna experiment with it a bit more before dumping it but this time only with condom because I don't think it's very hygienic to keep using this for a longer peroid of time without condom.