On a general note, I've been sent over 5 Chief OS's in diamond plastic, and they do vary even with similar colors. The flights are slightly inconsistent, often times ending up with either a flippy or overstable one.

But with that being said, I bag both flippy and overstable Chief OS's, and they're an amazing disc! If you are a tomb lover that wishes they were slightly straighter, this disc is for you.

The Chief OS is a shallow beaded putter.  Mine is in the Diamond plastic which feels great, it's firm and has good grip.  The Chief OS feels pretty good in the hand as long as you don't mind a bead.  It's pretty much board flat.  I was looking to use mine as a throwing putter and since I putt with Wizards I was thinking the Chief OS would feel pretty similar just a little more shallow.  Off the tee it flies ok, it has pretty good glide, but I was surprised to find that it was not very overstable.  It has a little bit of fade at the end of its flight but it does not have much high speed stability, so it wouldn't fight out of a flex shot and instead it would just hold the anhyzer line.  It didn't seem to fight the wind too well and I couldn't rely on it for throwing forehand since it just doesn't have the torque resistance.  

I think this would work fine as a putting putter for some people though for me it's a bit too shallow.  If you like throwing the slimmer profile putters like a Maiden or Swan, you might like the Chief OS.  Just don't take the "OS" too literally, this disc isn't exactly a Zone or a Harp.  

Another great putter from Gateway. Or is it a great approach disc? Why not both? Great for throwing off the tee or for upshots, or as a putter if you prefer. Almost wish they made it even more OS. It has a consistent fade, just not exaggerated like a Devil Hawk or Pig.  

I received a 175g Diamond Chief OS prototype in a mystery box a while ago and didn't know what it was for a long time. My best guess from the depth and rim shape, as well as the flight was that it was a slow speed, medium glide midrange disc. Before knowing what this was, I would have guessed the flight numbers were closer to 5/3/0/2. I could throw this disc farther than any putters I owned (my max distance was about 350ft at the time and this could push 300ft). The diamond plastic is feels durable and is easy to grip. Thrown flat and hard, this would push straight for 80% of the flight and then slowly fade to the ground. For a putter, it might skip more than you expect. The comparisons with a Harp in other reviews seem accurate to me, but I do think this is a faster disc than the Harp. 

My brother gifted me a 167g Diamond Chief OS a few months ago and that is how I found out my prototype was a Chief OS. The two discs have the exact same mold and fly exactly the same (with the lighter weight taken into consideration). I was very surprised when I found out this was a putter and when I saw the flight numbers. I like it for hyzer approach shots, flex lines (this disc will fight out of just about any anhyzer), and overhand shots. It is also excellent in windy conditions. Unlike other reviewers, mine have not lost their flight pattern. Maybe I got lucky or maybe the Diamond plastic is the way to go with this disc. I think it is a great disc if you are looking for a slow OS midrange or fast OS approach/driving putter. 

I have only two criticisms. The first is personal preference. I don't love a big bead on discs that I throw hard, and the usefulness of the Chief OS is lost if you can't throw it hard. I prefer the Prodigy A2 for this reason but if you don't mind a bead, maybe give it a shot. Second, I do think the flight numbers are not representative of the flight pattern. Oh yeah, and this is probably not a beginner disc.

I own this disc in HD Hyper Diamond and it is my main approach/upshot disc. I throw it FH and BH for anything out to about 200' on many angles - flat, hyzer, and mini flex shots on anny from a stand-still. The HD plastic is very hard but also feels super durable which I hope will hold the overstability for a long time without wearing too badly. Grips well in the cold and has quickly become my overall favorite disc.

The regular Chief is my main putter, but I will reach for the OS Chief when putting into stiff headwinds, and it works well.

I aced a hoe with this disc playing my first official round with this disc. It feels good in the hands, easy to grip, and very predictable. You put a fair amount of power into the disc before you begin to see any turn, based on how much power you can throw with you know exactly when this disc is going to hook up to it's reliable fade

Like has been stated by others the Chief OS is similar to a Harp or Zone.  Feel wise I think it is shallower than both of those discs.  Its depth feels close to that of the Shaman.  The Suregrip plastic does beat in quickly, so it is easy to cycle different wears for this disc. If you like the Zone or Harp but want something that is shallower and easier to grip, give the Chief OS a shot.