Yes, Leadinfo can be used legally under the General Data Protection Regulation (GDPR), which applies as European privacy law of May 25th 2018.
Leadinfo uses the visitor's IP address to obtain company data from public sources, such as the Chamber of Commerce. The IP address is personal data under the AVG, and its use requires a base under this law. The base used, is the "own justified interest" (Article 6(f) of the GTC). You are allowed to work with personal data without permission, provided that this serves a clear interest and you must take privacy into account.
Marketing and analytics are considered to have a clear legitimate interest, and Leadinfo uses only very limited personal data. IP addresses are not retained and only general business information of companies is provided to users. This has been done with regard for privacy.
As a user of Leadinfo, you should mention this in your privacy statement. You must also record in the register of data processing that you work with Leadinfo.