It is rather pricey, but so many people are praising it. I personally think its worth a try. I bought the whole mass stack from ebay for a pretty fair price $79.95 plus shipping for all 3(Nitrix, NO-Xplode and Cellmass)
I'll start using the stack like next week when it arrives, I'll probably write my own review on here also...to help out others. I did a review on NO-Xplode a while ago, but it didnt work for me back then. I'll see if it will work with the whole stack this time. Actually come to think about it...back when i used NO-Xplode I used to get the feeling that my biceps are so huge that I couldnt bend it properly do that kind of stuff, it felt like my biceps were too big for any kind of motion...I didn't get that feeling since...i didnt pay attention to that back then...but this time ill pay attention to any little detail and write a review :D
anyway...here's the link to the ebay auction of the mass stack...I think its the cheapest you can get anywhere.
http://cgi.ebay.com/BSN-MASS-STACK-NITRIX-CELLMASS-NO-XPLODE-GET-BIG_W0QQitemZ5613163277QQcategoryZ19261QQssPageNameZWDVWQQrdZ1QQcmdZViewItem