I like that you can choose the hardness/softness of the lead you want to use and have a pack of replacement erasers on hand. You can go into a Staples and get some B or BB leads for them much more easily than trying to get a #1 Ticonderoga which in fact you have to special order from the website.
Your big choices are the width of the lead. 0.5mm is the thinnest and excellent to write with. 0.7mm is a bit bolder but not messy. 0.9mm starts getting to be a bit much and I don't really recommend them. This is a personal choice or course but I recommend sticking with .5 or .7.
This pencil has been with me for years and I like it a lot.
I do detest disposable mechanical pencils. They just take all the fun out of the game and feel like awful pieces of plastic and, worst of all, they lack character.