This is only my opinion and others may vary. IMHO you need an EFI controller even if you leave the bike stock. They already come lean from the factory.
When you start changing things and allowing more air in and more air out, it gets even leaner.
The question to me is the cost of an efi controller worth the added security of knowing that If I make a run up into the mountains am I going to make it home or burn a hole in my pistons?
I realize with the economy being the way it is people are trying to save a few pennies and things like the SERT are kind of expensive....but so is the bike.
I would rather spend another few hundred on my several thousand dollar bike now to prevent having to spend several more thousands later should it be running too lean and hot. Personally, for me I would not even mess around with an EFI fueler although many will argue.
Do it right or leave it alone, something I picked up from my dad somewhere along the way.
As mentioned others opinions will vary quite drastically, with my CVO Fatboy I had over 36,000 invested in the bike, whats another grand one way or another to have a SERT and a custom map made for me on the dyno?
Maybe you can get by with a race fueler, the question to me becomes for how long? Will you possibly need to rebuild the engine sooner than if it was mapped correctly by a professional? I don't know the answer and I for one am not going to be the "tester".