Meaning I can know in advance whether the incoming transaction (API or form) is up to par with my requirements, at least based on what I've read so far. Ok, I'll start investigating the technicalities of this. Thanks to everyone commenting here 
Why would someone use this service instead of just broadcasting that TX to the network ?Because broadcasting the message to the network [as I understand it] requires the user to be connected to at least one peer in the network, meaning a different kind of protocol to handle.
Having a service that will broadcast your transactions to the network for a small fee (if the transactions are not small ones) requires you to compile and sign a transaction, and send it to the broadcasting service via HTTP, very straight forward for client-side clients and thin clients.
I can get on the Bitcoin network, find 3 peers and broadcast my transaction to all 3 then disconnect. In less than one second. There is no need for an external service, unless you are offering something extra, like anonymity.
First of all, yes. These kind of service will offer better anonymity than what you get with the vanilla bitcoin experience.
Second to broadcast the transaction to 3 peers you need to connect to a different protocol which can be problematic at certain situations, and it's not exactly a "fire and forget" solution, because you have to check that the transaction was broadcasted, and if not, you have to do the procedure again.