Hi all - new here 
As a test manager who’s been in the testing industry since 2001 I have some thoughts on this. I’ve only ever taken the ISEB Foundation course, that was back in approx 2003-2004. I don’t believe they are essential to the growth and development of a tester but I do agree with the sentiments above that they are a signal of an invested interest in development.
Would I mandate a tester attends the ISTQB? No. Would I support them if they expressed an interest in the qualification? Yes. There are many ways in which a tester can develop, I see this as one of those but wouldn’t prioritise it above other training such as technical training or mentoring.
I also haven’t found the face I don’t have the advanced certifications as a barrier to new Test Management or Test Leadership roles. When you have experience and examples you can talk through certifications become less important in an industry such as ours.
The bottom line, however, (and my opinion) is that these qualifications have zero bearing on how good a tester or test manager becomes.
Simon.