I ended up selling my 503cx to go with an etrsi outfit. I would have gone with an sq but I don't print square, and while I enjoy composing on a square screen it's just a waste when I end up cropping it down to 6x4.5 anyhow. I'm sort of backwards, I hated my hassy. I found a million reasons to just hate the system. Now that I have a bronica, i'm finding that I hate it just as much.. Buyer/Seller remorse. Try unlearning how to use a hasselblad, it's freaking impossible. Nothing else feels the same.
I don't know if the SQ back system is like the ETRS system, but the etrs system sucks. The backs have things sticking out that I know i'm going to break at some point. They don't fit into the body well at all, at least not on mine. With a hasselblad, you don't force anything. You don't need to. With this etrsi, I have to smack the back into the body. People whine about loading film into a hasselblad back? This bronica insert is so freaking fiddly..
Don't let all of my negative comments turn you off from what you want, my perfect camera doesn't exist.