The process for managing my certs was seamless as I had used it previously with other companies we worked at in our industry so there wasn't anything new or different about how they addressed security concerns compared to previous employers.
Their customer service can be slow going when trying resolve issues outside their system but once you are through talking directly from an account rep everything goes smoothly again. It would have been nice if some more cert types were supported like DER format instead only PEM which isn't ideal since not everyone has access to those files anymore (even though its easy enough convert them). We haven’t seen any benefit yet over using Microsofts own online tooling/system however I suppose this could change after implementation depending on what kind of support needs arise down the road.