I found this disc (tried the number on the back, but no response), so maybe it's more beat in and understable than a new one would be, but my first try on a flat throw it dived hard to the right (against the right-to-left wind) and cut-rolled so badly that it started coming backward to me again. After getting more of a feel for it in different wind conditions and throwing speed/angle, I have been able to make decent use of it: tailwind throws would give me a straighter flight and still reasonable distance compared to other drivers that would fade out (or require a much wider hyzer path) and/or lose momentum sooner; the 6 glide on the Underworld I think helped it stay aloft a bit longer to make up ground on the other drivers that would normally give greater distance. Same thing if you don't have the wind and throw it on the right hyzer angle; still a challenge if you put too much force on it, as its understability will turn it over too much, which makes this a better beginner disc. I'd probably rate a bit higher if it were in a different plastic, but these base ones get beat up pretty easily, and this is a disc that can't afford to become more understable; or if I were better at controlling rollers, I'd probably rate this higher, too, as it could probably work well for those types of throws.

I often find myself handing this disc to beginners who play with me for the very first time. Most of them have a very heavy hyzer release and the under stability of this disc gives them a feel for the S flight a disc should have.
For me, this is a utility disc when I need to anhyzer out of the rough, or around an obstacle, and still need a bit of distance. If I really rip on this disc it is likely to cut roll or stand up on the rim and roll with very little predictability. This disc also does well if I want to throw BH but need a FH flight pattern due to its under-stability.
Solid disc, it has a spot in my bag as the "utility disc" and there is most definitely a learning curve to it but for certain shots and situations this does exactly what I need.

I found one in a fairway this summer. I don't know how, but this particular Underworld has gotten less flippy with use. It used to be just a roller disc for me, but I'll often grab it off the tee for a beautiful S- Curve shaped shot now.

I really like it!

I'm a complete beginner. I bought two disc bundles(8 total) and this one was by far my favorite of the bunch. My natural release is a terrible nose up hyzer. As I worked getting my nose down I could get this disc to hyzerflip consistently. It would then drive further than the distance drivers I had in my bag. I one time released truly flat and it scared me to see how far to the right it turned before fading back in a S turn. It took me a second to realize I actually threw it flat. Eventually I want to try to throw rollers with it. 
 

Since it was from bundle it came in a grassy green that is begging to get lost. I will replace immediately if I haven't already bought another in a more premium plastic. 

This has turned into one of my favorite understable fairway drivers. My origio burst one has seen enough action that I'm considering getting one in a more premium plastic, since mine is starting to beat in pretty aggressively. But the hyzerflip lines with this disc are easy to execute at different speeds and the glide carries it a pretty good way for a disc on the slower end of the fairway drivers. If you are looking for effortless hyzerflips to anhyzer in a fairway driver, this is the mold to check out, especially for beginners.

This is a pretty fun disc to throw.  You never really know what you are going to get with Westside discs based off flight numbers.  This really isn't as understable as the numbers suggest.  I was expecting a roller disc and it isn't that bad.  

I really love the 7 speed disc range, it works perfect for my arm speed.  I don't have to really mash on something to get done what I need.  This disc feels great in the hand and has a real nice gradual turn to the right for a RHBH throw.  Throw with a tailwind, it flips up flat and finishes with a soft fade.  The distance is a little tricky, because it either keeps turning and eventually goes into the ground or it fades out.  It is hard for me to get a real long S turn for those big distance shots.  This fits better for me as that tight wooded shot or a shot that I need to finish right without a sharp fade that my FH would normally give me.  

I have forced this into some roller shots and have been very happy with it.  I'm hoping to beat this up a little more and make it a permanent roller disc for my bag.  

I would recommend this disc for a new player or someone working on throwing a BH.  This disc would be a great starter disc for someone or perfect for someone who throws on a steep hyzer angle with their BH.

Excellent disc that's useful for players of all skill levels. I have an Underworld at 167g in VIP plastic; it's a blast to throw, feels excellent both in terms of grip and plastic feel, takes dye well, and can be used for utility shots if/when your BH form causes it to regularly turnover. It's a fun disc to practice hyzer flips, rollers and lately I've been enjoying throwing it FH on holes where I need to throw something US on anhyzer.