I must say I'm really impressed with this formula! In terms of longevity, pigmentation and it's smudgeproofness - it is very on par with my holy grail Koji Dollywink Liquid Eyeliner. It stays put all day until you go home and wash it off, it is super black in one application, goes on really smoothly without skipping and dries really fast. Even with it's waterproof formula, I have absolutely no issues removing it. The applicator of the Stila Stay All Day Liner is a marker-like tip and because of this, I think it'd be really good for beginners as the stiffness can allow you to 'press' on your eyeliner when it's on it's side. I personally prefer a flexible brush applicator because that's just what I'm used to but I don't mind the foam tip.
From the above picture, you can see at the very tip it's starting to fray. This isn't really an issue for me as I like my liner to be a medium thickness, but if you like a really tight and thin line, it might not be as precise. Another thing I noticed when I first started playing around with this is that the felt tip kinda hurts when you line your eyes. When I say hurts, it's not that it's unbearable but it's a little uncomfortable. I think this might be due to the way I line my eyes and when new, the applicator is stiff. After a couple of weeks use I can safely say it doesn't hurt anymore - I guess you just needed some wear and bend to lose the stiffness :)
Just a quick comparison of the Stila vs Dollywink as I know the Dollywink is a holy grail for a lot of people out there (hollaaa). You can see that the tip's are very similarly sized, the thinnest line you can get our of both and the pigmentation/darkness are on par! The only real difference that comes to mind is the applicator. The Dollywink is a brush applicator and is much more flexible whereas the Stila is a foam, marker-like tip making it a little more stiff.
If I had to describe the Stila Stay All Day Liquid Liner in one word it'd definitely be "reliable." It is super black, smudgeproof, budgeproof and waterproof - lasting you all through the day and night. It retails for $32 at Mecca and comes in 15 shades!