They'll sell you avionics but won't do electrical design work or harness fabrication that involves SDS or EFII. From their policy:
1-Steinair, Inc offers specific and limited support for the SDS/EFII system(s). In all scenarios, Steinair, Inc will NOT supply any design guidance (panel, electrical, labeling, etc.) This will entirely be up to the customer. Steinair, Inc will NOT provide any wires related to any/all portions of these systems.
I went with Pacific Coast Avionics. No complaints, reasonable price and pretty fast turnaround. I ended up doing the electrical design work and wiring myself and really just needed someone to design and cut me a panel and then supply me the avionics so could've went with Stein, but PCA ended up cheaper by a bit.