We use it and they do work. There are several brands of this type, some of which can be installed thru the valve stem.
The kind we use is in tear-away bags. You just drop the entire bag into the tire during mounting, and as soon as the tire starts rolling, the bag disintegrates, and allows the balancing compound to roll around. This method works for those who are buying new tires and can have it installed at time of purchase. For those who are wanting to add it to their campers/vehicles after mounting, will need to get the kind that can be installed thru the valve stem....and not have to pay the price of having the tires dismounted/remounted.
Now, a warning. Moisture is your enemy. It will make some of the balancing beads/compounds clump up like a brick.......but I think with the Dynabeads brand, it doesn't hurt them physically, but the water would still interfere with the free rolling path that the compound needs.
You need to make sure the tire is dry before installation. Use any bead lube sparingly, as to not let it get inside the tire during mounting. You also want to make sure any time you add air, that it has a water filter/separator on it, to not allow water to be inserted into the tire. Oil from the air compressor can also get into a tire, if there isn't a good filter in-line somewhere. The oil will cause the balancing compounds to really stick together.
NEVER, and I mean NEVER use a fix-a-flat product if you have this form of balancing compounds inside your tire.
The jury is still out on using these if you have a tire pressure monitoring system (and a corresponding sensor inside on your wheel). Some of the manufacturers say their product will work with these sensors without clogging them, but we get notices all the time warning us not to use them with the sensors. Also, I don't think you can install a lot of these products thru A TPMS stem that has the sensor attached on the inside, due to the size of the beads/etc. To err on the side of caution, I wouldn't use them right now if you have a TPMS sensor INSIDE the tire.
FYI: Lead weights are being fazed out due to environmental regs. They are making the weights out of steel, tin, and/or using these kind of balancing compounds.
Expect to see the cost of balancing your tires nudge up a little.
These bags of balancing compounds that we use in dually tires cost me $6 per bag. You use one bag per tire. It costs me more in material cost per tire than using lead weights.....but I do save on labor costs, since I don't have to take the time to put the tire on a spin balancer to balance it.
On one other note: Dynabeads are loved by the motorcycle community, especially as hard as it is to find a place that can balance motorbike tires. My brother swears by them, as he has put them in about all of his 12 bikes.
2011 Flagstaff 831 RLBSS
I used to be addicted to time travel, but that's all in the past now.