Bearing in mind strictly legal criteria, we can confirm that Lucky Patcher is legal. However, if we understand illegality as any action that involves breaking a few rules (even if they don’t figure in any laws), then we would have to admit that Lucky Patcher is not legal.
In turn, it also infringes the conditions of the applications that have enabled different restrictions that can only be unlocked by making in-app purchases, such as getting rid of licenses or removing adverts. That’s basically how developers manage to finance their work so you would possibly be breaking a few intellectual property laws in certain cases.
In other words, nobody is going to call the police to arrest you for downloading Lucky Patcher but how legal or illegal it is will depend on how you use it: you can’t compare cloning an app to have it twice on your smartphone or tablet, to not paying to use a license.
It’s also quite complicated to get caught using this app so it’s really all down to an issue of ethics: it’s up to you whether you prefer to pay to make use of somebody else’s work or steal it for free.