I tried out the Underworld in Recycled Muovi plastic, around 170g. This disc was pretty understable for me. If I am throwing at max power, this disc will always be a roller. Even when I released it on extreme hyzers it would turn over and crash, or even roll still. If I took quite a bit of speed off, it would give me a nice S flight. For my arm-speed, it is a little too understable for me. 

As a roller it is an awesome understable option that will finish right relatively fast. I roll quite a few discs, and the Underworld isn't a roller disc I would choose for distance, but it does have a very fast and dependable right finish. There are a few holes at my local course where there are obstacles, ceilings, or mandos where you want a roller to stand up quickly and finish right, and this disc is great for that. For the longer, straiter holes, it turns over a little too fast. For distance rollers, I would be choosing something more stable that would hold a cut longer. 

For beginners I bet this disc is awesome. If I had picked one up when I had started, I think I would have loved it. It is pretty understable, and has good glide, so it is relatively easy distance.

I could see myself trying this disc for tunnels, at lower than max speeds, but I just don't think I would be able to throw it consistently. I normally have a disc like this in my bag, for right finishing rollers, but I am currently using the Hatchet. Having the Underworld in my bag with the Hatchet would be a little redundant. 

If you are looking for a lower speed understable driver with good glide, check out the Underworld. If you have a decent arm-speed and are looking for an understable, right finishing roller, this could also be the disc for you.