To preface this, I've just ordered some 20 packs of different picks in order the find the "one" that fits me and my playing style (I played an ESP LTD EC-1000 in Standard tuning, I couldn't test this with heavier gauge or a 7-string guitar).
I test all picks with the following parameters:
1. A fast/heavy metal song
2. Strumming songs
3. Practice pick, ala scales up and down
4. Slow song that requires exact attacks on phrases and is not "shreddy"
This is a SMALL Jazz III pick (not the XL version), so if you're not used to the miniature size of the pick, this will come as a surprise.
To get this out of the way immediately: if you do not like small Jazz III's (it's worth to give them a shot), this is NOT a pick for you.
Regarding the testing, this pick is simply amazing in all of those segments, but with a slight twist. The tone you get from playing with this pick is rather "thumpy" and not as attack/aggressive-heavy as you would with a Hetfield Ultex pick, which is to be expected.
Doing pinch harmonics with this pick is so so easy, but that applies to almost all Jazz III picks.
This pick is almost the same as other Jazz III's, however, this one has the most grip I've ever seen on a pick. This is almost sandpaper-like grip. However, this can also be a bit of a double-edged sword, as if the pick gets slightly misplaced in your hand (it causes more issues than a standard pick would due to its miniature size), you need extra effort to put it "back in place", as grippiness is then working against you. However, once I got used to the size of the pick, fast playing was so much easier than almost any of the picks and it rarely "falls out of place".
My personal preference is that I would pick the Ultex Jazz III XL over this pick for my playstyle, but if grip is what you're looking for - look no further, this is THE pick for you.