What are they? Do they work? What brand to use?
I asked all of those questions and decided to find out for myself what worked.
A regular sugar drop that is translucent and I'd say off white. It's a large sugar crystal to be sure. The ingredients list glucose as the priming agent. One drop is listed as sufficient to carbonate a 12 oz, and two drops sufficient for a 22 oz. The internet has reported fair to good results with this product. The main comments/complaints were that it did or did not work; on a product like this I tend to blame user error. I had an easier time getting these into bottles because it was only one drop to spoon in.
A small opaque white drop that is about the size of a skittle. The priming agents are dextrose, dry malt extract, and heading powder. Three to Five drops are the recommended range for a 12 oz bottle, no conversion is provided for a 22 oz bottle but one could surmise 6-10 depending. I found that 3 drops were too little, for average carbonation. I preferred to have 5 or 6 in a 12 oz bottle. I have made both full and part batches with this product, and I have seen good results. I have not experienced what I considered an off flavor as a result of using them. The internet has reported mixed results with this product ranging from: worked great, to didn't work at all because of no carbonation, floaties, and/or off flavors. I think if you have a good process, use really clean sanitary bottles, and good sanitation you'll be fine.
(read more after the jump)
Why these products might have failed for some people:
Under carbonated: used too few droplets; achieved less carbonation as a function of yeast v. sugar. High gravity beers tapping their yeast out; if your yeast was at it's alcohol tolerance this wouldn't have carbed regardless of the product you used. Extended lagering; if you cold shock chilled the yeast out of suspension, you may not have had enough yeast to do the work they needed to do. Extremely flocculant strains; I've heard of these strains floccing even before fermentation is done and needing to be roused before finishing. If your yeast have fallen out of suspension you might not have had enough yeast to get the work done.
Off flavors: Unsanitary practices in handling or bottle washing, bad luck.
Floaties: undissolved drops, if you can see floaties through the bottle try agitating them, I've done this just to make sure the most sugar is getting used and my beer carbs. Works fine. The oxygen that is in the bottle is in the bottle, live with it, agitating it once it's capped probably won't be the reason your beer tastes like cardboard.
My Two Cents
Both products work fine. Once I dialed the smaller drops in to get what I wanted from them they worked fine and the beer tasted good. The larger drops offer less customization but are harder to mess up. The use of these products makes carbonating a 6 pack of bottles from a 1 gallon fermentor as easy as falling out of bed. The attention to sanitation and detail which is important in every beer is especially important in small beers.