Without having looking into this, could any of it be implemented in a nice web interface where people can request proof of funds of your company and then you get back the results showing the BTC is indeed there, or you need to do some convoluted things? Since this is aimed for the general public to check funds of a company, not to generate your own cryptographic proof only, it has to be well presented to the average joe.
I looked at some of them, and in most cases the answer is no. A web interface can be made for requests, but you are not going to get responses like that. I'll give you a specific example for OutputZero:
Private key must be hot.
To have a live connection to a key and generate proofs on demand would be an extreme security risk. What companies can do instead is to provide quarterly proofs or something like that. Someone just needs to set a trend going with these things, with a few companies doing it regularly and it would move mountains I believe. I'm pretty sure that most people are not aware of any of these tools, or that you can even prove something like this without revealing information about it.