I bought these bags to store winter clothes, save space, and protect my jumpers from moths. They arrived this morning and I have tried a couple of the smaller size bags out on some jumpers. They are very simple to use - put the jumpers in the bag without over-filling it, and slide one of the white clips along the zip to close it. Now unscrew the plug in the valve, you can take it right off, put the hose from your vacuum cleaner over the valve and switch on. A few seconds later your jumpers look like a pack of salami from the supermarket! I was amazed how much they shrink down. Finally, replace the plug from the valve. It's a one-way valve so you do not have to worry about air going back in to the bag when you switch off the vacuum cleaner. Obviously only time will tell if the jumpers come out OK in the Autumn, but I don't see why not.
I notice that another reviewer had problems using these with a Dyson. I have a Dyson DC-20 vacuum cleaner and it works fine with that. I just removed all the attachments and put the end of the hose over the valve on the bag. Easy. The valve itself is about the size of a 2p coin, so just check your vacuum cleaner has some kind of nozzle which will fit over a 2p coin.