Just today noiced an advert for the Easy Bike in Moto Sprint (I had never noticed it before) and they seem to have a racing version as well as the 2 you mentioned.....

I've just spoken with RapidBike dealer in Poland and I think I have some more clarity about RB, so:
1. RB Easy - its basically Kev Mod without Oxygen optimizer, what means Kev O2 mod is needed to control AFR in both loops. RB dealer did not recommend this module for xt660z
2. RB Evo - its functionally equivalent of Kev Fuel Mod plus Oxy Optimizer. It works differently from Kev's devices. It builds 2 separate maps for both loops....and to my suprise this solution is also not recommended for xt660z, as this is enduro/adventure bike (varaible conditions - temp, fuel, filtetrs, dust etc) with narrow band oxy sensor, what means that autotune is ca 100-150km (in off road condition can change 1000 times during 100km)
3. Solution which is recomended is RB Evo + autotune module with wide band sensor (oryginal sensor stays as it is). Check is 50 times per second, so even if your filter goes dusty, or temp drops down by 20C or anything else, than values will be adjusted immediatelly (as I understood there is constant comaparison with AFR values saved in table)

Cost in Poland:
1. 240EUR
2. 520EUR
3. 780EUR

Kev - for your information - RB dealer said, that you can decide, what is your desired range of AFR. If you want to go power-side (lower) or economy (higher)

For me - te only solution which gives Kev's flexibility in adv riding (PCV is not an option) is RB plus second oxy sensor, but price.........