They are actually different
Hello Stoney,
I spent time talking with both companies before going with SDS.
EFii specializes in a turnkey version of the SDS computer. EFii installs the magnets in the flywheel and welds the injectors in the intakes and does the complete wiring harness for you. However, all capabilities of the computer are not available. I choose not to list the capability differences because my information is a year old. Do not assume Robert merely purchases a computer from Ross and the systems are identical. Robert has chosen many sensors, mounts, and fuel pump designs to meet his requirements.
SDSefi sells you all the components to include a jig to install the magnets, a wiring harness to your specifications and no need to weld in the injectors because they developed injectors that use the ports above the intake valves.
There are very useful computer features that were not available on EFii a year ago, but I can't guarantee they are still unavailable. Ross did offer to install the magnets for me, but I decided to use his supplied jig and it is very easy to do. He supplies the instructions, jig, drill bit, tap, allen plug and magnets. The only thing you add is a small bit of epoxy. When I say the components are very complete I mean VERY complete. I had to cut down a socket to install one component then later found that Ross had included the cut down socket in the box. Everything you need is included.
Customer service - both companies are very active. Robert answered every email and phone call rapidly. Ross or Barry would return emails I was merely putting in the que for normal business hour response. Both companies understand homebuilders work on weekends.
With that said, I went with SDSefi and am very glad I did. I suspect many EFii owners are equally happy. It is a tremendous amount of information to comprehend with variable fuel input and variable timing, but the factory support is amazing.
The first time you push the start button it is all worth the learning. It starts instantly and purrs.