Brosef-
IT would take me 2 pages to list the cars/engine I have assembled/tuned/wrenched on, but JUST in tuning experience, I have dealt with AEM (For Mitsu, Ford, and Hondas, ProEFI, DSMlink, RoM Burning for Mitsu, Nissan (fixing bad Jim Wolf tunes), and Bosch ECU's, Motec M2R, M400/600, S300, Chrome, 034, AutronickSm4, Ecu Editor (Suzuki) Powercomanner PCII, and IIIusb, Megasquirt Pre-fab and built it yourself, and Simple shit ike AFC I, II, and NEO, Translators on DSM's and Buicks.... and some Im forgetting.
Also, I think its safe to say I have made more power with Trucks, Cars, and Bikes, than anything in you line up. Its safe to say, I'm more qualified to answer this question than you are to question my answer.
Also, I am very good friends with the man that has, arguable (would not be much of an argument) the Fastest, and highest horsepower street S4 in the whole god damn country. You know how many wide-bands it has logging, and displayed so as you say "find it useful for at a glance reassurance during pulls. " Zero. Not a fucking one. You know how many times it has fucked up being flogged and DD'd at near 800 whp? Zero. Not fucking once.
My philosophy is simple one; Different is cool, and going fast for nothing, reliable, is the proverbial holy grail-but never over-think the machine, and you'll never forget where your going or where you came from.
In that mindset, the answer of why, in my opinion, you don't need 2 widebands, or wideband readings visible at all times should be easy one to decipher. Unless you are trying to make north of 800whp, and/or have full control of all cylinder load fueling parameters separately (in which case you should have a pyrometer in each tube anyways) I feel its not necessary.
But if you are into blinky gauges to look at making you feel like your in a real bonified race car, by all means have at it. In that case I'd recommend the AED UEGO-usability, and bling factor are unmatched at the price point. And, you can add a wideband controller to log both banks at once without the use of the FM unit.
Brosef-
All in good fun Jones.