I just installed the BMS Stage 1 piggyback in my wife's X1 (28i). We have the N20 (not N26) and thus utilized all 4 connections. Took about 45 minutes - easy. No CEL or anything. Only had to reset the clock and good to go.
First impressions: lots more pull. Neck-whipping acceleration in the higher rev-range. Seems very balanced, as you can meander around town with fuel economy in mind... then stomp on it and really feel the added hp/tq.
Can't imagine what Stage 2 will look like.
Well done Terry and BMS!