I have! SymbiFlow is very good for being a FOSS hardware toolchain, sometimes it has trouble with peculiar FPGA primitives but it's nothing you can't work around.

I've hacked around with my EOS S3 board less than my other boards (mostly because if I need a CPU I'll just add a VexRiscv soft-core in a regular FPGA), but I can definitely see it's use case if you'd like to accelerate sections of your software without building the entire design on an FPGA.