Should we use stuff like that?
That is entirely up to you to figure that one out.
The two usual concerns are
1) You get banned for using it.
Personally I still go with "you mod, expect a ban, any online you get is a bonus" but some seem to find the self directed hiding, contriving means of stealth and general apathy on Nintendo's part (they could find you out no problem at all if they were actually determined) seeing them stay online for a while after modding as bans are not a thing, and to be fair the timeframes involved are not inconsiderable where you can be hacked and still enjoy online.
2) Some kind of moral issue, maybe with a side of legal question in some scenarios.
We can do the piracy = theft, copying, unsanctioned playing... debate if you like and what people think there. Want it as a demo, were never going to buy it, were always going to buy it (maybe even preordered if they are silly meaning Nintendo technically already has their money for it*)... all those are modifiers in this beyond "don't care, playing it anyway".
*we saw a debate earlier in the thread on this actually. Someone was quite insistent that owning a legit copy (or effectively so) still does not mean downloading it (or some other "illegal" means of obtaining it) is allowed. This is debatable on multiple fronts; the law does allow for backups but does not necessarily specify you have to do the deed yourself even if companies really want that hurdle of you needing to be hacker/electrical engineer, and there is the "what harms are done" question that actually underpins civil law which is presumably where the interactions fall (the state does criminal actions, individuals and corporations suing each other for money fall under civil law) and again they already have your money under some scenarios in that. That also says nothing about terms of service and enforceability thereof.
Third being if you are silly enough to grab this from a torrent or similar that can be traced back to you but that seems like a moot point.
Spoilers being made are a thing but that is always a problem; some retailer breaks street date, some guide maker publishers sooner... avoid spoilers however you normally do being the only real response there as even without a leak do we have to wait for some timeframe in the future for people to have played it (first weekend, end of month, is there a holiday time period any time soon...).