Indy is a very large and complex set of complicated classes. In many cases you need simple things. Why use the very large Indy? Use the small Synapse! Synapse is very simple and maximally versatile.
In my opinion, Indy and Synapse are for different purposes. This is the reason why I developed Synapase. Synapse is complementary to, and not a replacement for, Indy.
And IMHO Synapse is much better, with nearly 100% compatibility between Windows and Linux platform. Indy has a lot of problems with the Linux platform!
Synapse also works with Free Pascal and Lazarus which opens up more platforms for your code to run on.