I am thinking of lying into SJU and taking intercarribbean to EIS. Cost of ferry and taxi to ferry is almost the same as a flight $117 Is their reliability reasonable?

I think IC probably cancels about a third of their flights. I haven't checked for a while. You can check how they are doing now on the Flight Aware site.

This used to be my "go to" but I wouldn't do it anymore unless it was significantly cheaper. Recommend flying into STT and taking the ferry or private water taxi.

In my case "free" flights from MCO to SJU then pay for flight into BVI. Ferry costs at STT are about $80 so the extra amount may be worth it.