First off, the color selection is one of the better selections in the 12/0 and smaller size thread range. (I personally tie about 75 to 80% of my flies with their Violet, which is more of a burgundy than a purple, unless I am marking the heads with a different color thread to denote various weight designations, as is the case with weighted nymphs and the likes, but my point is that there's a ton of color options, not that I use them all). Second, the strength of this thread is simply outstanding - both when compared to its 12/0 rating, and just its strength in general. I'd compare the thread breaking strength to that somewhere between Uni 8/0 and Uni 6/0 (I use Uni only because they are a more common thread on the market), and this is for the SemperFli 12/0 thread. Third, this thread splits like a dream! Simply spin a few turns counter-clockwise, then take a needle / bodkin and insert into the thread, and viola, you have an evenly divided thread! Fourth in my list of major qualities I look for in a thread, the bulk accumulated when tying with this thread is minimal. If you desire bulk, get a different thread, like 3/0 or larger. This bulks when you use half a spool of thread, but you really have to work at it to get any kind of significant bulk and build-up from the thread. Really love this thread. I was a Uni lover for the longest time, before Veevus came out and SemperFli came out. Loved Gudebrod threads, especially their 10/0, but alas, they closed shop a few years back... then I was a Veevus lover, before I was introduced to SemperFli 12/0 and smaller, but for the above reasons, SemperFli 12/0 is finding its way onto my bench in increasing quantities. If you tie a lot of flies in the 12 down to 20 size range, especially for trout or grayling (possibly smaller, but my eyes don't do well tying smaller, personally, even with cheaters), this is *THE* thread I recommend for you!
