I've owned three mice with the philips twineye, two of them being Razer products.
The steelseries sensei has the same amount of z axis distortion as the twineyes, and so do most mice I know of. This is in normal use and in me trying to lift it up. Those people are either EXAGGERATING IT, haven't turned off acceleration so it looks worse (while they're in motion) or genuinely got bad sensors (not that likely as it would act up in other ways).
There is no point torturing yourself with a generic mouse, I cannot use them anymore personally, so I would recommend getting the G500. Furthermore, I assume in your area Logitech is much more common than the Rat mouse so you'll have more options in locations to buy, they're probably even available in big department stores' electronic sections.
Therefor you should have (at least) a 6 month warranty which is valid (the mouse offers more but the laws in most countries is the store has to offer a warranty) if you buy it from a big department store or a reputable seller who has a warranty system.
Therefor in the OFF chance you get a faulty mouse/sensor you can return it.Random useless bs:
IMO the rat mouse is also very comfortable and has lots of customization but it is seriously uneeded. Most mice are exactly in the acceptable weight range and you adjust to them anyway. A LIGHT mouse with terrible grip points compared to what you're used to using/doing with different angles and shapes may be harder/require more force than a heavy mouse perfectly contoured to you. these are extremes and most mice are tailored to this.
An example is my third "gaming" mouse (when I got into pc gaming) was the mamba followed by me trying the orochi then moving to a roccat kone, steelseries WAW mouse and finally my steelseries sensei, the orochi was HEAVY for it's size. however it was small and the gloss is grippy, more grippy than the rubber sides of my light sensei, so they require about the same force but in different locations.
During my mouse switches within two days I got "used to it" through extreme changes and now, using my sensei for a week, I'd say I am 90% back to my aiming skills in BF:3 with my previous mouse, however in a more comfortable palm grip (imo fingertip is great and all but tires me >2.5 hours straight late night school days
) so changing mice won't be a problem if you don't like it./Random useless bs:
Now, since you said the price isn't an issue, I'm sure if you genuinely hated the mouse for whatever reason or if it was faulty and for some reason you don't have a repair/replace claim you can replace it easier. This is more so with the cheaper and more available g500! You can do so with great choice in Christmas time, or you can setup an aramex account like me or even switch up mice.
GL, have fun