TheKey seems like it focuses mostly on China or Asian countries. So there is a limited use case there already.
Selfkey is using self-soverign identity (SSI's) as the basis for creating a marketplace of services/partners. The idea itself is good but self-soverign ID's are difficult to implement successfully.
Civic probably has the best marketing strategy of the lot, but is lagging a bit on the technological innovation side.
There are 3 huge drawbacks for all of them:
1. The validation/verification part of KYC - it will still need manual user intervention. Either you will need to go to one of their designated partners or they will come to you (KYC.legal takes the latter route).
2. An assumption is - the party you interact with will need to be also enrolled on the platform. E.g.: if you have a SSI with Selfkey and you need to interact with party X - if party X itself does not have a Selfkey SSI then you are stuck.
3. A further assumption is that there will be widespread adoption....ain't ever going to happen. All fintech or companies requiring KYC or AML compliance - need to do independently - especially if they are operating under a strict jurisdiction /regulatory framework. Large fintechs would want participation and influence in the design of the algorithms and mechanisms. To make matters worse - smart contracts are still considered experimental so, which multi-billion corporate would leave their reputation to chance? Some ICOs might use these solutions, but I don't see any fintechs who would take the plunge.
Lastly - most of them use blockchain/DLT as a facade for some new cutting edge innovation. Rather, they can be achieved with "traditional" technology. The only difference is - you, as the end user will have to purchase their specific token to interact with the platform.
If you gave me $1,000 and ask me to invest on any of the 3 listed above - I'd give you $100 more and ask you to buy 2 ETH
