If you're wondering if you need a leveling tool, personally I don't think you do. Do you want one, though? Probably ;-).
Features and Benefits:
• Aluminium Alloy Outer case
• Three spoked food-grade 304 stainless steel base
• Size: Easy to read depth markings
I have to admit, I'm a fan of levelling tools like this, there's just something particularly satisfactory about spinning a metal thing on the top of your portafilter, and the nice level surface it leaves behind.
You don't really need a tool like this, if you see a pro barista using one (some do) and ask them why they use it, if they're honest they'll probably tell you because they enjoy using it as part of their work flow.
If you asked them if they didn't use it, would the shots taste any different, at all, an honest barista would probably laugh, and say, nope, not at all, but it's fun.
If I'm not in a rush, and I just want to enjoy making my espresso, I'll pull out all the stops, WDT, spinny leveller tool thingy, maybe even RDT (spraying coffee beans with water for no good reason), and then the tamp - purely because these things are satisfying, regardless of whether they're all truly necessary.
So, there you go, you don't need one, but what's that got to do with anything? ;-).