An EULA is a license agreement - a contract of sorts. Breaking a contract you agreed on is punishable in court under the right circumstances, but it's not "illegal" (otherwise, you could literally make up new laws). EU courts often find EULAs unenforceable due to a host of reasons (we're very consumer-friendly over here).

Furthermore, you are only breaking the contract if you accepted the contract in the first place; so it only covers what you can do with the product iff you purchased the product (and accepted the EULA that comes with it). So if you are doing blackbox reverse engineering, there is nothing the company can do to prevent you from figuring out how their physical product works.

Finally, as another comment noted, in most parts of the world reverse engineering for interoperability purposes is protected by law.

In many parts of the world reverse-engineering for the sake of interoperability is legally defended right, and any such clauses of the EULA are void.

Breaking an EULA isn't breaking the law.