#1: Duck feathers. Yes, decades ago this was made from duck feathers, this stopped long ago, today it's made from l-Leucine is obtained by fed-batch fermentation with E. coli NITE BP-02351. Btw, if you use "vegetable gelation" capsules, those too are made fed-batch fermentation with E. coli. The E coli are genetically altered to produce in one case vegetable gelation and in the other, L-Leucine which is then extracted.#2: Made in China. Most of the world's pharma feedstock is made in China, end of story.#3: Taste: Ranges from salty/bitter to "not so good," to "horrible." Answer find something to mix it with, pre-fill (as I do) 00 capsules, or use an oblate wafer (a thin piece of dissolving paper made from potato starch, one or two grams goes well into the flat type, more than that use the pouch-type.#4: Can one take too much? Yes: "“ Based on recent research, an upper limit of safe intake (ULSI) for leucine is proposed for healthy adults: 0.53 g/(kg·d).”It's nice to be able to buy this enormous amount of pure amino acid for such a low price. End of story.I was impressed by Bulk supplements..this is first time I ordered this from them! Great & now I use my old container to put it in..I read that taking leucine prior to a fasted workout reduces muscle loss while allowing the desired fat burn. I assume it works, but have no evidence to support or refute that claim, so my review is not on the effectiveness of the product, but other qualities of this purchase.I tried it this morning, and as other reviewers said, the taste is pretty bad, but tolerable (as I assume all leucine powder is). I just drank it in water. It mixed OK. A flavored 0-calorie beverage may mask the taste better, but I'll probably stick with water. It's a very fine powder so was hard to avoid puffs of air blowing it around a bit. Again, I assume this is normal of pure leucine.The packaging is simple and seems it will last through the use. It doesn't come with a measuring spoon so I used one from something else I had and hopefully it was the right dose. That's no big issue since I always end up with extra scoops of all sizes from other products I've used and it keeps the packaging flat and the prices low.I also like the concept of BulkSupplements providing pure individual supplements vs branded, marketed, and over priced combinations. As I believe other BulkSupplements reviewers have mentioned a few times, the company sent me an email after my purchase and offered to send me something else for free if I agreed to give it a fair review. I thought that was pretty cool (and probably explains why there are so many reviews) and since they didn't directly try to coerce me for a good review, I don't fault them for this form of marketing. In any case, I'm trying something else from them so stay tuned for that review after I get it.BCAA's (Branch Chain Amino Acids) have been show to be critical to anyone trying to build muscle. Research has provided evidence that "fasted" training (working out after not eating for 6-8 hours) is a great way to burn fat. Unfortunately, you can also end up burning muscle in the process. Many already know that an extra dose of BCAA's post-workout help build muscle. Fortunately, recent studies have shown that BCAA's taken before your fasted workout will help maintain muscle. And more specifically, L-Leucine (one of the three main BCAA's) in doses of 3g -5g. If you go with BCAA's you need to take about 10g to get the 3-5g of L-Leucine. Or, you can just take 3-5g of pure L-Leucine - which is a lot more economical. So I take about 4g of this stuff before my morning workout and throw another 3g in my post workout protein shake (most whey powders have L-Leucine already, but typically only a couple grams).Now, one warning if you are going to follow in my footsteps...this stuff tastes pretty bad. I first tried just to mix it in water and choke it down. It does disperse in water ok (doesn't clump), but it tastes horrible. I've now gone with a low calorie lemonade mix instead of water. The bad taste still comes through but it is much more tolerable. I don't blame the company for this, as I assume this is just an unavoidable characteristic of this particular supplement. However, BulkSupplements, if you are reading this...anything you can do to make this stuff taste better would make this a knockout product at a great price.ExcelenteThis product has a horrible biter taste and is not mixing well with water. It is the nos disgusting taste that I have in a supplement