I may have never had the opportunity to own an expensive mouse, but if you told me that this mouse costs only 30€, I would say that you are a liar. Having tried many Razer mice, this one has pleased me the most.
Positives:
It has an excellent program for customization, where you can adjust everything.
Very good RGB lighting with a variety of effects through the program.
The fact that you can change the side buttons as you wish (MMO, FPS, etc. by adding 2 buttons, 3, etc.) makes it a "poor man's" Naga Trinity. A unique feature for its category and quite impressive.
It reaches up to 10,000 dpi through the program, and I don't need to say anything else. (For those who are bothered by the fact that you can't set the dpi to, for example, 3675 and you can only set it to 3600, go play with Playmobil. You think it makes a difference.)
Good choice for people with large palms.
Ideal weight, preferably for gaming (comfortable).
Negatives:
It leaves discreet fingerprints, but again, for 30€, it's fine.
I had difficulty finding the program for customization, but it's actually on zero-ground.com (a quick Google search like: zero ground niiro ms-3700 micros, you won't find it).
The side buttons are not as good quality as the regular clicks, but again, let me remind you that the mouse costs 30€.
For some reason, the lights don't turn off when I shut down the PC, and I have to unplug the USB at night (but again, I'm afraid I might be missing some setting).
I've been using it for a month, and I want to see how it holds up over time... so far, take it without hesitation. There's no reason to spend more, even if you can.
Edit: After six months, the scroll wheel broke. Although I can press it while scrolling, nothing happens. It simply stopped working while I was on the internet (maybe the plastic inside broke because when I move the mouse, it sounds like maracas). It has many flaws for its price, and I expected it. So, if you want something temporary, go for it. If you want something for everyday use, look for other mice in its category.
Edit: A friend of mine who bought the same mouse a few months after me experienced the exact same issue with the scroll wheel. It seems like it's not just a defective product, but a general flaw. The reason reviews exist is for the reader to make a decision on whether to buy it or not. Well, I do not recommend it despite its many positives. Spend an extra 10€ and get something else. From Razer to Motospeed, you will find much better options. It's not worth the risk, as it seems like it will break in less than six months.