CO2 Bottle ???

Hi,

Anyone ever used one of these, could sumone tell me, does this let out co2 when it needs to, ie, measring what in the air???

Thanks

Here is the link..

http://www.hydroponic-shop.com/product_info.php?cPath=33_81&products_id=950&osCsid=c87c85abe9cd439cc355809ae9f86ef6