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This Matt Cutts video is from 2013, but I think it still applies today. I ran into the same issue once re: terms & conditions, asked a question very similar to yours, and somebody on this message board shared it with me. Hope it helps. Long story short, as long as you're not being spammy about it, you should be fine. I would add that since it's actually useful to your user, I would implore you to include it!

Could you possibly add a line or two by each client? It could serve the dual purpose of getting some content in and enticing the user to click on the case studies. I'm not a fan of content just to have it, but that recent Whiteboard on "cruft" comes to mind and I wonder whether it applies here. Would be interested to see what others think.

https://moz.com/blog/clean-site-cruft-before-it-causes-ranking-problems-whiteboard-friday