That sounds like it could potentially stop the employee from undertaking similar work should he leave the company.I remember this clause or very similar from thirty years ago, working as an employee Civil Engineer.
If you develop something possibly based on knowlege gained as part of your employment and it would assist the employer in his business, ie he could develop an income stream for the company using it then where ever or on what device it was developed on he may claim an interest. Mostly unless it was within the normal business of the company he / they would not.
I thought those kinds of clauses were not legal in this country (aka non-compete).
You can't legally prevent someone from working in this country AFAIK. Ie you can't force an engineer to work in McDonalds rather than continue to be an engineer for another company. The above clause could potentially prevent that former employee from working in a related field (either for himself or another company).
"Knowledge gained" doesn't even have to be inside secrets in this clause - it could be literally anything.