Yup, MBPR early 2015 so TB2, my cheapest option is the i-tec thunderbolt 2 dock which is about 40% cheaper than OWC in my country.
I am aware of the power issue because i'm using my audio interface via the adapter which can be normally bus-powered from FW800 and i gotta use an external power supply anyway.
My guess was that all those "thunderbolt to XXX" adapters are not just adapters but just external PCIe cards since ethernet or FW aren't contained in TB standard(unlike DisplayPort for example), therefore it doesn't matter if they're connected directly to the port or daisy chained, but just wanted to make sure before purchasing the dock.