What are the pros and cons of diversifying across robo-advisors?

A robo adviser is alway removing human emotions and helping you to diversify in a low-cost way.

I don't see the point of diversifying if your capital or monthly amount is small. You should probably lump into one for easy checks. (Do NOT check daily, investment should be long term, check once or twice per year... easier said than done thouhg)

Stick to one. Find the best that suits you and stick to it. Any small disadvantages or advantages that crops out later probably is insignificant.