Not sure about the quality, but the school is not recognized by the Swiss central government, so degrees may not be acceptable in some employment situations. According to Wikipedia, it is licensed as a university in Malta. Not sure if that adds anything, though.
Earlier threads https://www.degreeinfo.com/index.php?threads/anyone-heard-of-the-european-graduate-school.26612/ https://www.degreeinfo.com/index.php?threads/any-advice-about-the-european-graduate-school.21470/