t3ase,
Check out this thread for a list of know cartridges that are compatible with the HB.
http://www.slybaldguys.com/smf/index.php?topic=10630.0. Scroll down to the fourth or fifth post (from Tyler). Personally I have just fallen in love with the Gillette Custom Sensors carts. They are a good balance between not too many blades and ease of cleaning between passes.
...Let the M5 discussion continue.
t3ase,
Check out this thread for a list of know cartridges that are compatible with the HB. http://www.slybaldguys.com/smf/index.php?topic=10630.0. Scroll down to the fourth or fifth post (from Tyler). Personally I have just fallen in love with the Gillette Custom Sensors carts. They are a good balance between not too many blades and ease of cleaning between passes.
...Let the M5 discussion continue. 
Yeah, sorry. I completely misread the original post. Just went back to read it again and wondered wtf I was thinking.
Razor x, the own brand M5 razors are the same as the normal razor, the only difference is the packaging.
Picked up some of the Dollar General carts a few days ago, the brand name is "dg". Upon visual examination they appear to be exactly the same as the originals including the color scheme. When I shaved with one it was like coming home.....no discernable difference. The only problem is that there are only 2 carts in the package and they sell for $3.50.
At CVS & HyVee 4 are $7. When I run out of carts I'm gonna switch up to the M5 in black & blue. That's what they sell at HyVee. Switch it up a bit.