Some are, but most are available in the typical weight configurations. If you want more weight, you can simply add more weight to the insert.

One advantage to many of the 2-blade designs are the thickness of the blades. Thick blades do not bend as easily when they hit bone. This can make a big difference on a less than optimal hit. However, putting a skimpy 100 gr 2-blade head on, doesn't offer much advantage other than possibly a bit more penetration on good hits.

There are tradeoffs with each design. None work best in all situations, though most work adequately when the hit is a good one on a medium sized animal like a whitetail. Most rib hits with a two-blade should be passthroughs unless your setup is a very low energy one, or something's not tuned right.

In general, more blades increases the momentum it takes to get a passthrough. More blades usually equals a greater chance of wind affecting their flight, bone deflecting their path and their thinner blades breaking. On the plus side, more damage is done per inch of penetration and the wounds tend to bleed longer when using more blades .

For me, hitting the ribs exactly where I want and getting a complete passthrough, usually results in a deer that dies within 7-14 seconds. The thick 2-blade designs usually give me the best chance of this happening. This year I'll be shooting the thicker Muzzy Phantoms in their 2-blade configuration out of both my recurve and my compound.