I have had excellent results with the Rover MEMS2 as used on the MPi. I think it all depends on your expectations.
I was hoping the SC solution for the MPi would give similar results...I am not sure it has.

I know you asked about the SC ECU swap for the SPi, while I don't have an SPi, I know someone who tried it and has since moved on.
Terry

Are there any FI owners using the Specialist Components injection and computer? Reviews? 

Having worked on multiple SPi and MPi cars I've found both to be above average when it comes to reliability and drivability, when compared to the rest of the range of carby minis. Just be sure to get a good one to start with, as chasing down issues on one that's been butchered could prove costly and time consuming. Most parts are available for both Spi and MPi setups. 

I have a 94 SPI. It is my only car. It's almost 30 years old. Do you know of any person driving a twenty nine year old English car, let alone a mini? I don't think there is any person worldwide but Please chime in if you are another nut.

The SPI starts every time. Everything else falls apart or fails like the rubber parts. Those vacuum elbows in the engine bay are the first to go. Next the cones, then the knuckle boots. I can go on and on, but these are the trials of owning any mini.

I remember my experience with carbed minis is hard starting and the smell of gas.

I have had three spi cars. All were very reliable. 

I'm looking for a classic Mini, and seeing a lot of them have EFI.  After driving an MGA and an MGB in college, I'm skeptical of something as complex as EFI on a British car that wasn't imported and supported in the U.S.  For those of you who have experience with them, how's the reliability and are parts available?