When NYX do something well they completely nail it. Where there's a high end cult product NYX can usually produce a similar product for a fraction of the price and not bad quality. The Jumbo Eye Pencil's fall into this category and though I have definitely found fault with them I keep using them and getting different colours and can see myself getting more.
What's good? These can be used as a liner or an eye shadow and it's the flexibility of these that I love. Most days I scribble one of these (preferably youghut or iced mocha) all over my eye lid and blend it out with my finger but if you want more intensity you can do a really good line along the the lashes. If you don't like wearing a lot of your eyes a line with the right colour one of these will make your eye colour really stand out without looking very over the top. You could also draw a heavy line along the lashes and smudge it upwards over the lid for a really effortless smokey eye.
The range of colours is pretty incredible and make these a great choice for those who want to be a bit more experimental with colour but don't want to shell out a ton of money. These are highly pigmented so they are great for pro kits who want loads of colour to work with and won't cost the earth. I don't use that many bright colours so I love having a couple of these to hand just in case.
They are reasonably long lasting - I use them as a base and put shadow over the top which means they stay on all day. A lot of people like to use the colour 'Milk' as a primer to make other colours really stand out.
What's not so good? A lot of the ones I've tried are definitely more sparkly than shimmery which will be preferable for some, but not for me. As far as I can tell you can't sharpen these. I've yet to use one all the way down (when I have I will update this post). So I imagine these will either involve wasting a lot of product or a lot of plastic packaging. (*UPDATE 2017* you can sharpen these if you use a midsize sharpener like the one from Nudestix)
High End Comparison: The most similar product to these are the Charlotte Tilbury Colour Chameleon pencils which I love. The CT colours are chosen to match specific eye colours and are not unreasonably priced at £19. You can also sharpen the Colour Chameleon pencils so you get to use nearly all of the product as a pencil. However, the sheer variety of colour from NYX means you should get a very close match to the CT pencils and you'd be able to get 4 colours for the price of one Colour Chameleon. All the Charlotte Tilbury products I've used have been very good quality so I do think you get what you pay for. I do also think that you don't need to always spend a ton of money on products.
What You Need to Know - NYX Jumbo Eye pencils