SO a bubble counter will just let you know how much gas is being put into your tank by providing a visual reference: bubbles per ______ (second, minute)...
Check out this link for more on gas separators...
http://www.plantedtank.net/forums/eq...r-diy-c02.html
And look through the DIY section (or better yet do a search) and you can find a plethora of ways to make your own, home-made bubble counter/gas separator!!
And that check valve you linked to should work just fine (as long as it will work with your size tubing)