Blockchain certificates are offered more on online video tutorials, you'd probably liked it to be video online for you can keep reviewing the video and ask the video tutor for support if you find it difficult to understand. Unless you just download the course from torrent sites you don't get support but Udemy teachers offers support when you subscribed to them.
I'm aware. But those are just certificates which are not as great as a degree, in my own opinion. With either a Bachelor's Degree or Master's Degree in Blockchain technology from a reputable college or University, you'll be able to stand among other professionals in the industry. Mainstream companies will give more credibility to Blockchain Experts that have graduated from a mainstream University, than those who not. We're still early to talk about this, since Blockchain is just 11 years old. I think that's a short amount of time, for someone to become an expert in the field (although Vitalik Buterin is quite knowledgeable about how Blockchain works). Over time, we'll be able to see mainstream Universities offering Blockchain degrees if the need arises. As long as there is money involved, you can expect a degree of anything today.
Nonetheless, both Udemy and Coursera seem to be solid platforms which provide serious education about Blockchain technology. They're a great choice for becoming an expert until mainstream Universities start offering Blockchain degrees to the world. So far, there's only one University (University of Nicosia) which has started offering a Master's Degree in Blockchain technology (as far as I'm aware). But I'd expect renowned Universities like Cambridge University, Cornell University, and even MIT to start offering Blockchain degrees sometime in the future.