Firstly, any signature product you buy will not somehow magically make you sound like the artist in question, whatever the name on the lid promises, because most of that sound comes from the artist's hands and not yours or mine, so it's best to approach the EVH 5150 OD with no preconceptions of what you think it should sound like, and take the approach of how you can make it work for you.
The EVH 5150 is called an 'Overdrive' pedal, and generally speaking, overdrives are designed to push the front end of your already crunchy amp, which this pedal will do very well if you back down the gain setting and turn up the volume. Where it really shines is when you put it in front of a loud clean amp. In this case you can start turning up the onboard gain pot and get bags of Van Halen type saturation that stays defined and detailed with plenty of attack at the front of the note. Basically it can take on the role of a distortion pedal rather than an overdrive. The pedal also comes equipped with bass, mid, and treble passive EQ to give extra versatility and ability to refine a sound that works for your amp and guitar set up. So rather than think you are going to automatically and instantly nail Eddie's tone, consider the 5150 OD a versatile pedal that is more than capable of getting you a great Rock tone, no matter what guitar or amp you own (within reason). In theory, the pedal should get you in the ball park of the different eras of Eddie's sound and Eddie Van Halen doesn't allow any product to go on sale with his name on it unless he has had a large input into the development of the product
Over to the far right there is small push button labelled boost. This little button gives an overall push and compression to all your settings which means more volume, gain, bass, mid and treble. The boost function can add another voice option, if you experiment with your settings a little, possibly backing the gain down, you can get a more compressed woody tone, demonstrating another side to what the pedal can give you.
So it's an overdrive, a distortion, a boost pedal all in one good looking box. It can also clean your signal up with an onboard adjustable noise gate, which will take out any unwanted hiss and noise generated at extreme settings or by using it with an already noisy amp. A certain amount of hiss is generally acceptable whilst playing, but due to the high gain nature of the pedal and style of playing it's more than likely to be used for, the adjustable gate is great inclusion. Wind it all way back and it's bypassed, the further clockwise you go, the quicker and harder the gate hits, glowing yellow when it does so.
An onboard 9 volt battery will give you a respectable number of hours use if you want to make it portable, but many will live in a pedal board and be hooked up to a power supply. True bypass switching keeps your signal clean when the pedal is not in use completing the package.
Any product with EVH written on it tends to be a great quality item, whether it be the pedals guitars or amps. But as I said earlier, they should be purchased with your head rather than your heart. That means don't buy something just because Eddie uses it, buy it because it's going to work for you, and give you a tone you are happy with. This is certainly a good versatile pedal that will, in the right hands, deliver some huge Rock tones and enhance most set up choices.