Hi slammer187, we have never met but I think we now some people in common.
I have just had a look at this bivi bag and it works out at around 14.50 euro delivered. That is a great price for a bivi bag delivered in Ireland.
If you buy a used bivi bag on ebay you will pay around £30 sterling which is nearly 35 euro. You will then have to pay around £10 sterling shipping so you have now spent nearly 47 euro. You have been advised that if you buy a used bivi bag that you will need to reproof it. Buying a bottle of tech wash and then TX direct will set you back around 20 euro. So thats around 67 euro spent on a used bivi bag. To me its a no brainer, I would buy the 14.50 bivi bag and take a chance. Worst case scenario is that it does not work out and you can put it on ebay and will probably lose out on around 5 euro (the price of a pint in Dublin). You have been told about it from someone who actually has used it and user experience must be worth more than opinions gained from looking at an image and reading a description (no offence intended to all the people who posted). If you are still not happy to purchase this bivi bag then some research will lead you to better value than a used bivi bag I am certain. In fact the forum you saw the link for the cheap bivi bag also has links to new bags at a selection of prices from a reputable supplier.
Hope this helps.