supergrippen,
i can vouch for the ESS kit after having experience and sat in one of our forumers 528i with the ESS kit complete with bigger injectors and full ESS programing about a week back, its a perfect setup, No CEL, No lean issues, idles like normal, just perfect.
i always have doubts about getting software from abroad of which i personally had a bad experience with TMS and dinan on my e36 328, eg, idle issues, low spots and performance overall. and forget about getting a piggyback to do the work, our local tuners here sucks bigtime and they know nuts about tuning continentals. But having sat in this ESS kitted car, i am just sold...the car is a perfect gem, runs like a stock car from factory at startup to about 1500rpm and with the mash of the pedal or a downshift of gears turns the cars into a bullet train, the torque just kept propelling the car all the way til 235kmh and that was only til 4th gear at 4kplus rpm, more to go but had to slow down for a turn off to our exit. the road was also a short one, from the desa hartamas overhead bridge til the jalan damansara turnoff, so you can imagine the performance..oh did i mention this is also a automatic 5er.
anyway if you are interested in getting the ESS kit for your car, i think you can contact him as he is getting a ESS dealership account with them, i think he can even install the system for you which he did on his own car. he is kinda anal to the tiniest details even to the extend of ceramic coating the aluminum colour parts to satin black just to make the whole engine bay looks like its as it is from the bmw factory. so i think you will be in safe hands... you may pm me for his contact, nice guy, not a mech but very technically inclined.