Recently I ordered 2 ADA pollen Glass diffuser 20's from
Aquarium Design Group.
Thjese units have done very well and look very nice.
All in all, I'd say these are worth the added cost based on overall quality and durability. They do costy more, and they are not for everyone, but they are certainly a few steps above many of the cheapy stones/disc etc.
I give a great deal of weight to a good CO2 system.
That is one area I demand good performance.
So it might be worthwhile to consider these and the Ruby, this is a very nice very cool device. Again, perhaps 2-3x more than some other brands, but very nice.