If your talking about the Cree and Seoul emitters from vendors like dealxtreme.com, then I've heard that they are pretty durn good. Occasionally you'll get a lemon, so I'd buy 2 to make sure at least one worked. At $10-12 a lamp, thats still pretty good. Most of them are Surefire like in appearance -- strong hotspot with large circle of spill. However, they probably aren't putting out 200, or 270 lumens. Most emitter or bulb manufacturers test the light output at the emitter itself. By the time you factor in the reflector and head of the light, its lost a good deal of output. Surefire tends to conservately rate their lumens, so I'd trust them. The general rule of thumb is to mutiply a different manufacturer's advertised lumens by .60 or .65. Those are the real lumens, for the most part.
Me, id stick with Surefire.