Pros : Want to match just the right color? Want to just have fun? I used glow powder and various frits to make a set of galaxy knobs for my daughter's dresser and it worked perfectly with her room's decor. The bubbles even fit in as stars....
Cons : No weights given for filling, just "mound up the top" which you have to go OVER the top of the mold, or risk not being able to fit in and cover the hardware. Not what I was expecting... and these end up a bit heavy.
Other Thoughts : These get built up backwards from other frit projects since the bottom of the mold is the stem rather than the textured front. This can be a boon to those not used to typical casting, but makes it a bit messier to plan as things melt unevenly.
Also, be sure to use a good glue to adhere the hardware (it's going to be twisted a good bit!) and be aware that if you use all clear, you'll see the hardware through the knob.